The US System is very different from UCAS or any other type of system they offer abroad (to me). It's not like the college is going to send you a list of grades you need to get in order to get in, as I understand it is with other systems. They'll take a look at your transcript (I guess that would be your class grades, however they've done them), your SATs (SAT I and two SAT Subject Tests), your TOEFL if you're not a native English speaker, your essays, extracirriculars, and everything else you need to send in. Then you'll get a letter in April saying whether you got in or not.
The role that actual IB scores play in US Colleges is minimal. A lot of IB students here in America don't really do as well as they should, since by they time they sit for the tests, they've already gotten into their colleges. The only thing you can do with IB scores is that if you get a 5, 6, or 7 on a Higher Level test, you can get out of taking some classes once you're in college.
I suggest you do a whole lot of research if you're going to be looking at US Universities. It's not something you can decide to do on a whim; it's a totally different system that will not make much sense. In fact, if you're just deciding now, you're a little late in the game (I've already taken my SAT I twice, my SAT IIs once (Lit, Math II, and German), and I'm taking ACTs on Saturday).
Boston College is a pretty good school, but it is Catholic. Is that something you're comfortable with?