If you're a girl, as I am assuming you are, of course your chest is going to be bigger than the rest of your body. You are going to develop breasts as you go through puberty. In addition, I don't believe that your rib cage is huge.
Puberty lasts for several years. You won't stop growing as a girl until you're about 20, so relax. Don't get so hung up on your body. Just take note of all the changes that are happening and be thankful for what you were given.