According to the websites marines.com and officer.marines.com, you need an accredited 4-year college. A freshman through junior year student can through the Platoon Leader Class, while seniors and grads go to the Officer Candidate Course.

IIRC, you are a junior in high school. Get your grades sorted out, do extracurricular leadership-type stuff, do as well as possible on your SAT, and kill the ASVAB. Your HS football will help. A transcript that obviously shows you getting your head on straight will be noticed. Look for colleges/unis with NROTC programs, and try to get in them. Not only will this help pay for college, but it will give you an in to the culture (though not as much as Annapolis).

Your other option is hardcore old-school. Enlist, then OCS. Be a leader through basic and keep it up during deployment. Mustangs ftw.