You seem to have little or no understanding of what a mortal sin is. It is not some happenstance activity, like making a mistake. It is deliberate choice to reject God. It is for real; not just some silly superstition or some made-up rules to keep us “under the thumb” of the Church. and so if you reject God - whether that is an instant before you die, or years before you die, and you do not reconcile with God, then God loves and respects you so much that He will honor your choice. That is a point that people don’t want to deal with, mostly because they don’t want to take responsibility for their chocies. They always want to blame someone - their parents didn’t love them, or raise them right; someone else lead them into the sin (like they were dumb sheep, not individuals making a choice); the list goes on and on as to who it is we can blame, rather than taking responsibility for our choice.
God so loves us that he gave us free will - the opportunity to choose good or evil. And God so loves us that He respects the choices we make - a point that many try to deny, balming it all on someone else, when in fact it was we, ourselves, as individuals, who made the choice.
God does not play “Gotcha!”. He is not some distant, remote angry father, watching us like a hawk and just waiting for us to “make a mistake” so He can torture us. As found in Isaiah 38:17: “In your love you kept me from the pit of destruction; you have put all my sins behind your back”. And Isaiah was not a Catholic… but he, too, repented.