I am also a Junior in High School, and am trying to go to Annapolis. One thing that you should do is go there sometime and talk to some people that work there and went there. If you know of anyone near where you are that graduated from USNA talk to them. Also, there are admissions presentations that are held most days. you should definitely go to on eof those. go to this website to learn more about that.
http://www.usna.edu/visit.htm
I have talked to a guy that graduated from USNA and worked inthe admissions department for a little bit. he gave me some very helpful information on filling out the apps. if you hae any questions when you do them, just PM me and i will try to get an answer or good advice.
By the way, sign up to go to the Summer Seminar. There are 3 different week long sessions. you can go to any one of them. It shows to school that you are serious, and it gives them a chance to evaluate you before hand, which is very helpful for admission. You can sign up for it starting February. you want to sign up for it as soon as possible. They always have alot of people on there the minute the app becomes available. Three years ago the server crahsed because too many people were trying to do the summer seminar application at once.