He paid the penalty for sin committed in ignorance, not for deliberate sin committed after we are given the knowledge.
Many attempt to stretch “grace” to cover those sins, but there never was any offering therefor.
Read Peter’s and John’s epistles and get in line with what they show us.
Peter makes the point well that nobody is “saved” yet, but if we endure in his commandments to the end, we will be saved on that day.
Those who say they know and love God but do not love their brother are not of God, Those that went out from us never belonged to us, etc.
When a “Christian” walks away from what he has learned is the truth, he never was a Christian. We Christians are saved from the moment we repent and accept His gift. We do not have to accomplish anything to end up saved on that day, as you say. The twists you allude to are power levers for the Catholic Church to administer the Holy Sacraments and control people. I was raised learning the Catechism, with venial and mortal sins, the necessity of going to confession to a priest to have a mortal sin forgiven before we get hit by a bus and wind up in Hell, ad nauseum. That’s not the teaching of either Simon Peter or John, and certainly not of Jesus, but of the Catholic Church.
Those of us who are saved will live in such a way as to honor Him because we are motivated to please Him out of gratitude and love, not because we have to earn His salvation, because we cannot earn His salvation, and not because the risk of not earning His salvation is hanging over our heads every waking moment.
Teach your alternative gospel no more.