When Jesus is asked “Lord, will only a few people be saved?” He answers “Strive to enter through the narrow door" nicely dodging the question for those who love precision about such things. (Lk 13:23 & 24) John in his vision strives to see how many have been saved while granted a glimpse of heaven, but is likewise thwarted a census when the number is that "which no one could count." (Rev 7:9) Was it a small fraction of the seething multitude of the total human population over time? Was it everybody? No straight answers are offered.
Stuck in our desire to be in the know about who and how many will be saved, we're often presented with two viewpoints well illustrated by two early theologians. Origen erred on the side of Universalism, that in the long run EVERYBODY gets saved (apokatastasis), even the fallen angels, including Satan. So powerful is God's mercy and the saving power of the Cross that no creature can resist it. This opinion was condemned by the Church at a local council at Constantinople in 563. St. Augustine, affirming Salvation in Christ, however, saw us more in a "damned masses" situation, with those being saved but a tiny fraction of humanity. This line of thinking relies on understanding salvation as through an explicit Profession of the Faith and Sacramental Baptism, something the Church takes a more nuanced view of since Vatican II.
There is a current strain of Catholic theology, most widely known through the writings of theologian Hans Urs Von Balthazar (d. 1988), that says without denying the existence of Hell—which is a matter of Faith—we can reasonably hope that all might be saved: "This is good and pleasing to God our savior, who wills everyone to be saved and to come to knowledge of the truth." (1 Tim 2:4). God says, after all, "I swear I take no pleasure in the death of the wicked, but rather that they turn from their ways and live. Turn, turn from your evil ways!" (Ezekiel 33:11) Christ descended to the absolute bottom of our fallen-ness, even into suffering and death, so that when he was "lifted up from the earth, [he] will draw everyone to [him]self." (Jn 12:32). So among quite a number of theologians I respect (including Von Bathasar and Bp Robert Barron, along with some statements of St John Paul II) there exists the allowance for the hope, which avoids straying so far as the condemned apokatastasis, but does question the assumption of the Augustinian "damned masses" which to them seems too dark in the light of such hope offered by the Evangelion of the Word Become Flesh, not to "condemn the world, but that the world might be saved through him" (Jn 3:17).
All that being said, Christ is adamant about the particular and final judgment and the existence of Hell; in fact he talks more about Hell than any other Biblical voice. So Hell is real, no matter how populated it might be.
The existence of Hell is a necessary corollary to the teachings that 1) God is love and 2) we all have free will. We can freely turn away from that love, and existing through eternity with the door locked from the inside against love is Hell. The light of Hell's fire throws into starkness the necessity of using our freedom with aim toward our eternal destiny (CCC 1036). But there's nothing in the Church teaching that says anyone HAS to be there. I can't think of anything I've read that assumes the default state of any individual is condemnation to Hell (though there are some statements of Jesus on Judas that come awfully close).
The Fall certainly led to our slavery to sin and death, yes, and subject to concupiscence, sure—which left on their own certainly leads to a predisposition to willfully choose even Mortal Sin. But simultaneously the truth is evident that even from the moment of the Fall, God did not abandon humanity to suffer our Fallen state without offering grace. He calls out to Adam and Eve in the garden (instead of, you know, just immediately smiting them), God's prophecy of the proto-Evangelium, that salvation would come through a son of Eve, His clothing Adam and Eve in garments, the earthly salvation of humanity through Noah, His covenants, the Law, the Temple, and ultimately, of course, in His Son. There is no canonical list of the damned (Dante doesn't count); the Church affirms Hell's existence but also affirms in the Catechism,
"1037 God predestines no one to go to hell; for this, a willful turning away from God (a mortal sin) is necessary, and persistence in it until the end. In the Eucharistic liturgy and in the daily prayers of her faithful, the Church implores the mercy of God, who does not want "any to perish, but all to come to repentance":Ultimately, we must proclaim the truth and necessity of the both/and of God's justice and mercy, including the reality of Hell. Being Christian "impels [us] to act as witnesses of the Gospel and of the obligations that flow from it." But while we're compelled to bear witness to the Gospel, I'm not sure we need to dwell to much on preaching Hell. All but the most invincibly ignorant must see that evil is present on earth now, and if one refuses to seek after goodness, basic cause and effect tells us that a trajectory of evil will lead toward "getting what we deserve." Those with an atheist's materialistic viewpoint that refuses the eternal soul, at the very least, they're living in a world that contains evil now ... and without the hope of salvation, a cold, hard world without God is Hell (the door locked from the inside against Love, remember?).
Father, accept this offering
from your whole family.
Grant us your peace in this life,
save us from final damnation,
and count us among those you have chosen."
My point in all this is not that there is no Hell, (there most certainly is), or that it might be empty (highly unlikely) but for me that it tends toward uncharitableness on my part not to HOPE that Hell might be empty of human souls (the fallen angels are just screwed, consequence of a perfect intellect and will), and it's more important for us to proclaim the Kingdom (with the attendant need for repentance), which Christ commands (Mt 10:7 & Lk 9:2), while He's rather quiet on how much disciples are supposed to preach on Hell.
Overall, worry not too much about how other people consider the matter (unless they're speaking for the Church and outright denying Hell's existence); for yourself and those to whom God has entrusted you, hope in God's salvation and let that hope impel toward inviting everyone into relationship with Christ, work out your salvation with Fear and Trembling (Phil 2:12), and diligently Strive to enter.
Some suggested reading (and a video) on the topic:
- The Fall: http://www.vatican.va/archive/ENG0015/__P1C.HTM
- Hell: http://www.vatican.va/archive/ENG0015/__P2O.HTM
- Human Freedom in the Economy of Salvation: http://www.vatican.va/archive/ENG0015/__P5O.HTM
- The Gravity of Sin: Mortal and Venial Sin (esp. 1861) http://www.vatican.va/archive/ENG0015/__P6C.HTM
and "The Population of Hell" by Cardinal Avery Dulles which goes through a longer survey of the trends of theological discourse on the subject: https://www.firstthings.com/article/2003/05/the-population-of-hell