Score high on your SATs (yes studying is painful but worth it) and try real hard the remaining time you have left. You will be fine. Not to downplay the corp because I have a lot of respect for them and have considered doing exactly what you are talking about, but as long as you have a 4 year degree and are not a total idiot, I believe you would be accepted at Officer Candidate School or ROTC if that's the path you want to take.