International student-1st time giving ACT in December

So, I’m going to be giving my ACT with writing on 10th December 2016. My average score right now comes to 28.
I really need at least a 30-31 because my colleges are Vassar, Wellesley, Amherst, Smith, etc. And my SAT was a no show with a 1880 super score.
What can I do to increase my ACT score? Math is a huge weak point for me. Science- I am unable to do the last passage. Any strategies to do better? I’m working on my math.

science - look at figures and read info if only 100% absolutely necessary
math - can really only learn what you don’t know

Thanks!
Got a 28 :confused:
Science and Math pulled me down.