I think naturally as a composer, you should want to learn everything that relates to music, or things that inspire you. I am a junior in High School as well, and composition is also something i want to go in to, but theres a more important message that all composers should learn beneath all of the requirements. If you really want to be a composer, than you must never cut corners, must always believe in the goal you desire, and constantly learn new and interesting things for as long as you live.
In this day and age, many people seem to be undercutting their education based on the quick access to distractions. Don't be one of those people! If you follow those 3 concepts, you will not only get everything you need to major in composition, but will gain even more than you originally planned for. Dont be another person who fits the requirements, go above and you will not only feel ready for college, but you will be! Remember, you only go into college because you recognize that there are many aspects in music that you cant teach yourself anymore. Based on what you told me, you still have much to teach yourself, so i would focus on that right now!
So yeah, thats probably the best message i can give you for colleges. The rest is up to you.
-Jamal