Yeah, I was like that in high school, too. Never had to study, never even read the books. Straight As. I took a seven year break from college, changed my major to something that was a challenge and found out exactly how much I did not know how to study. And you know what? I learned how to study wicked fast!
It sounds to me like you want to do something better with your life. And looking at the Navy nukes is a good thing, I've never been in the Navy but having been in this industry, I've seen the good it did for peops I've worked with. When my grandfather started in the Navy, his family lived in a tar paper shack with no plumbing or electricity. While in the Navy, he got himself a degree, became an officer, learned how to invest wisely and became a very wealthy man. His life was enriched by experiences and opportunities that he would have never seen had he not been in the Navy.
I agree with hamsamich, you sound like you've got alot to offer. Go down and talk to the recruiter, see what they have to say. Find a book on good study habits. You're looking to make a change, because you feel you have a lot more to offer... listen to the samich, stop sabotaging yourself and find out how good you really are!