The short answer is that good grades in college will almost always completely overrule bad grades in high school.
Listen to EClaris on the being an asshole about it thing, and on the thing about the secondary school often being a better choice than the first. I was crushed when my first choice waitlisted me and my parents were opposed to pursuing it, but I went to my second choice and think that it's the greatest place on earth and that I would have HATED my first choice, and I'm pretty sure that this is partly because I came into #2 with no expectations and was thus pleasantly surprised by all the stuff I liked (versus if I'd gone to #1, in which case I would have been unpleasantly surprised by all the stuff I didn't).
Also note the financial advice there. From a purely numbers point of view, there aren't a whole lot of programs in the country that are actually worth OOS (or private) tuition, and most of those are pretty competitive. If you go to your #2 and hate it, try to transfer to #1, but bear in mind that student debt follows you everywhere and that most degrees help you out by existing, not by being from particular schools. (The existing part is also probably going to change in the next decade or so, but whatever)