Marks high enough to get into a good American university?

Grades and SAT scores are both important for the top American universities. Your current grades might get you into USC, but not Harvard/Ivies, Stanford or UCLA (since UCLA is much harder to get into if you're from outside California). Even perfect SAT scores won't help you if your grades aren't considerably higher since you're competing against the top students from the U.S. and other foreign countries. You may still be able to get into some fine American universities (and we have many), but probably not the schools on your list.