(As an American) In my schooling I was always told we won the revolutionary war mostly because the British would just stand in a line and shoot during combat. How true is this?

It's one of those things that starts from a tiiiiny kernel of truth and then got twisted around to kludge into the needs of teaching history. Given that you're not the first to question what you learned in school, here's what previous posts have to say on the matter:

u/BeondTheGrave addresses how the fighting went down;
u/tyn_peddler explains the military tactics of the day, ie why "stand in a line and shoot" worked during that era;
and there's always the FAQ section on Early Modern Warfare for more reading than you ever thought you'd need about warfare in general of that period. For covering the American Revolutionary War specifically, there's a sub-section below that.
On the matter of Braveheart With Muskets, this post from a now-deleted user addresses both your question itself and the movie.