Can someone please tell me why I got a 17 on my ACT..?

Try the SAT, it's easier in my opinion, and there's no science. You gotta take it quick though, and study for it. There's this great book out there called "Kaplan SAT Premier", "Kaplan SAT 12 Practice Tests" and "Kaplan "Reading Comp Practice" get those books and study, you'll do fine.