As for those kids who make fun of your bra size and tell you that you look "fat and ugly," are these kids whose opinions should be important to you? I know that hearing anything negative about one's body is not pleasant, especially at your age, but my guess is that the same kids who are making negative statements about you are also making statements about other kids as well. In other words, these kids somehow are so down on themselves or insecure about their own self-worth that they put other kids down as a way to feel more powerful. Try to let their negativity slide right off you and, if you can, forgive them for their insecurity.
My sister also got her period young and developed large breasts soon after. She got the same treatment you're receiving. As boys took more notice of my sister, her girlfriends became jealous of her breast development. Some of the girls even called her names. This was a tough time for her, as I am sure it is for you.
You have nothing to be ashamed about or to apologize for because your body matured earlier than usual. Your body has not caught up with your breasts, but it will. In the meantime, you might want to consider asking trusted older women family members or adult women friends to help you purchase bras that minimize the appearance of your breasts.
I can't tell you that your maturing early won't result in unwanted comments and attention. But I will tell you that things will get better as you continue to grow. You have a healthy, strong body. Feed it well, keep it active and listen to those friends who know and like you for who you are, not the size of your chest. Thanks for writing.