Maybe this will help: A Catholic view of “pre-destination” is that of an archer. We are the arrows that G_D shoots at the target. As such, we are all pre-destined to reach the target (heaven). However, due to external forces (wind, gravity, large birds-of-prey swooping down to knock the arrows off-path) not all of the arrows follow their pre-destined path and will fall short of the target.
The analogy breaks down because we, unlike arrows, have free will, and we can choose (regardless of the difficulty involved) choose to fight the wind, gravity, or large birds-of-prey (pray?) to put ourselves back on course, by uniting our will with that of the archer who launched us in the first place.
Oh, and thinking about salvation and fear: sometimes, I think those evangelicals who preach “Once Saved, Always Saved” (OSAS) hate the idea of a merciful G_D. It’s like they view G_D as standing on the edge of heaven, bouncing on His toes, just waiting to launch His Damnation Darts at everyone who sins, and the only way to keep from being hit by one of these Darts is to get a guaranteed authenticated OSAS Umbrella. Anyone who is carrying one of these OSAS Umbrellas is protected against a Damnation Dart because G_D then can’t see what you’re doing.
In my view, OSAS says since it’s impossible to know WHEN G_D will be merciful, then you CANNOT assume that He will EVER be merciful, especially to a sinner like you. The only way, the ONLY way, to assume mercy and therefore admission to heaven is to claim it in advance through OSAS.
Catholics reject OSAS. Our lives are a process, where we work, through the application of divine grace, to align out will with G_D’s will. If we consistently trust in G_D’s mercy, in that we believe and act on the belief that no matter how many times we fail we can still honestly seek G_D’s mercy and rise up again, until the moment of our deaths. Even if our lives have been one of sin, if at the moment of death we honestly repent and say, “My Jesus, Mercy” G_D will forgive our sins and permit us to enter eternity with Him.