Astounding, isn't it?
When Protestants have confidence in their salvation by God's grace alone through faith alone in Christ alone, Catholics charge us with "the sin of presumption," and we're anathematized and damned to hell.
Yet when Catholics say the rosary for 15 minutes a day, they can be "assured of their salvation."
My husband says he fled the RCC of his childhood when he was around 18 and realized very little of what Rome taught was consistent with much of anything, not even itself.
That is the blessing of being, and, especially, remaining, Catholic.
Any formalism that assumes you're saved because you do something - whether it's praying a specific prayer (or that generic "sinner's prayer), or any other action or attribute (e.g. intellectual assent) is in error.
One's salvation rests in God's election confirmed by endurance to the end. There is none of us 100% sure of our election, but we can be 100% confident in God's faithfulness. He'll save his people.