You REALLY do need to raise your scores and grades. I STRONGLY recommend you get a study CD for the exams, or take a course and really put effort into it. USNA and most of the better schools use the SAT/ACT scores in two ways... first, to see how well you performed on a standard test vs your peers. Second, the exams are considered predictors of how well you will do once you hit college level work. You should plan on taking them more than once. Also, be aware that there are differences between the SAT and ACT exams, and one or the other may favor you with higher scores. Once you get past the primary screening your high school grades will come into play.
Best wishes, but it really doesn't get easier as you go... If its worth having, its worth working for!