How do i become popular at school?

Im 13 and Im not popular at school and i already left a bad image of myself since i did heaps of embaressing things. Im really shy so that doesnt help. A number of people had already called me retarded. I dont know if its me or my looks or how i act. I also want to get the guy i like but thats a different question and its still open so if you can help that would be nice. I know that people say just be yourself i tried that and it dint work i tried to be someone im not and that dint work. Is it because i can never be popular and be a loser my whole life? I dont know... Please help thanks :)