Kai-- perhaps it used to be that way-- but the treatment of functions from a conceptual stance (rather than a procedural one), the inclusion of trigonometry, and advanced concepts which used to be in a rigorous GEOMETRY course, just to name a few differences. Some of those things are pretty old school-- and the sheer volume, pace, and rigor in the course catches many students off guard, and always has.
Val and I have both had recent (and not particularly good) experience with what passes for calculus preparation in secondary institutions these days.
My own story is much like Dude's, btw, and yes, it did result in imposter syndrome and math struggles that lasted for many years-- well into college. I should have had no trouble with calculus, but I did. Because it scared me. Looking back, my problems were related to the very rude(!!) shift in pace and work expectations, a truly dreadful teacher for the course, coupled with my previous beliefs about my math ability (accurate, but not useful in the context).
