What should I do?

Okay so since you're in your junior year, I would suggest signing up for like summer college classes, cus they're usually available to juniors and seniors. Second do community service whenever you can, those hours look GREAT on college applications. Be sure to study HARD for your act and sat, and retake them if you think your scores aren't as good as you would like them to be. Consider getting a part time job when and if you can, those look good too. Keep your grades up and take any ap/honors classes that you can either this year or next, or both. Maybe join some clubs like math club or smith nerdy or like a study club, leadership positions in those sorts of things always look good. As many extracurriculars as you have time for really, community service, a job, after-school activities, etc. etc. Also unpaid internships look FANTASTIC and will greatly increase your odds of getting into where you want to get into. Hope this helps!!