Wolpertenn, you're shooting yourself in the foot by lowering calories so much. The less you eat, the less your body will metabolize (while consuming muscle and retaining fat) and you will need to continue cutting just to maintain your weight. It's a recipe for disaster.
Since body composition is your main concern rather than weight loss per se, you should look into strength training to build muscle. Muscle needs calories - specifically protein - to develop, so you will need to up your intake significantly. Google the "New Rules of Lifting for Women" and the Strong Lifts program. The latter is designed for men, but you'll find forums where women discuss the program (and share some seriously impressive before and after pics). Both programs suggest no more than 3 x 30min heavy weight lifting a week for a significant reduction of fat/increase in muscle. I also recommend searching for photos of women at different weights/body compositions. You will be shocked at how much better the more muscular (and heavier) women look than the women who weigh less but have a higher body fat percentage. Don't obsess about the scale, it's all about the muscle!
I know firsthand the pressures on teenage girls to be thin (been there, done that!), but the fact is that severe calorie restriction is not only unsustainable and misery-inducing, but can actually sabotage your weight loss (and permanently damage your metabolism, making it harder for you to ever maintain a healthy weight). Keep researching nutrition and exercise and you'll have a better chance of reaching your goals in a way that is healthy, sustainable, and effective.