Am I too fat to wear a bikini?

Don't ever to think of yourself as "fat". Think along the lines of "beautiful" :) You're 13! You should just be having fun! To answer your question: you are not "fat" or "ugly" until you think of yourself that way. I say, if you want to wear a bikini, nobody is stopping you! Don't let what other people think of you affect the way you see yourself.