OK. First of all, I think you're way too concerned about body proportions. While certain physical dimensions can certainly enhance an androgynous look, most of us simply manage with what we've got. You can more easily adjust your fashion, though, and there's a lot you can do with it. Thumb through any fashion magazine and you'll see a number of interesting looks that are strikingly feminine or androgynous more from hair, clothing and accessories than the model's body. In fact, most high fashion models are chosen because they have somewhat masculine features.
Growing your hair to your shoulders will certainly help with the broad shoulder look. Hair that forms something of a vertical line from the head to below the shoulders can be narrowing. Wear vertical lines or darker colors on your shoulders and torso. Don't worry about your "postieror". I haven't seen you, but I suspect you don't need any surgery or medical treatments just for the purpose of looking more androgynous. Everyone is overly body conscious when their 18. No matter what you do, you're going to have to learn to love yourself as you are at some point. Remember that.
