It's definitely a good idea for you to start your college search now. I think you're a junior because of your age.
Firstly, there aren't many "scholarships" for composition, but there are many paying competitions that could become your savings for college. You should look for more playing scholarship opportunites. There's a thread on here that lists a few composition contests, but if you google it, you should find quite a bit more (Just be sure you look at the deadlines before you get excited

)
A few I know of:
BMI John Lennon Songwriting Competition
This ones really more for those who write pop songs, but priced at a $10,000 package, it's impossible to just turn away so quickly.
http://www.menc.org/networks/collegiate/bmirules.html
(Be wary, this only allows it to be used for certain schools. Most state schools are out.)
Morton Gould Competition
You might be a bit late for this one (I wanted to enter it too, but I didn't learn about it fast enough.) Any concert work is eligible. The money for this must be used to further your studies in music, which, in your case would be attending college.
http://www.ascapfoundation.org/gould-info.html
Lotte Lehmann Foundation Art Song Competition
You might keep your eyes on this one to see if it re-starts. You have to compose an art song, but I'm not sure about the other requirements.
http://www.lottelehmann.org/llf/programs/ascapllf/
Left Coast Chamber Ensemble's Ninth Annual
Composition Contest
An interesting looking chamber composition. It only pays $600, but every cent counts! Plus, you get a performance!
http://www.chambermusicpartn.org/contest.htm
Merle J. Isaac Composition Contest
$25 bucks to enter, but an orchestral piece for young students. It's a little close, but, again, you still have another year to get ready for college.
https://web55.mysecureserver.com/astawebcom...rings/merle.htm
Also keep an eye on the Enescu Competition, it seems like it's pretty prestigious.
Secondly, do you live in America? If so, the FAFSA should be your best friend. Also, look for schools that are interested in getting your instrument. They will usually have some money set away for scholarships for that particular instrument (That's one of the factors that my brother took into consideration when he applied to the school he now attends.) And never forget the other little scholarships you can find on FastWeb! They are definitely worth your time.
Good luck with your college search! Hope it goes well!