Your junior year is your money year. It is what your collages see, it is what financial aid will see, and it is when you take all of your most important tests (SAT, ACT and regents (for ny)). Hopefully your junior year is when you can bank on your credits, then you can make yourself a sick schedule for senior year, hell if you worked hard enough during the past 3 years, you can graduate early.
Basically, Junior year is not a year to fuck up, don't give up.