Get a tutor (or tutors), especially when you get to college, if the way the profs teach doesn't mesh with you. Many colleges have student assistance centers where you can find a tutor, possibly at no additional charge from your tuition. For that matter, consider getting one now, if it's feasible, to bring your scores up and improve your chances at getting into the best school possible.

I'm assuming that you're wanting to work in the technical/science side of NASA.