Why do I hate P.E at school?

Im a guy, 15 and I live in England. I really like secondary school but for a while now I seem to really dislike P.E. At primary school and my first year at high school I enjoyed it, but now I seem to dread it and try to get out of it whenever possible. I always hate playing sports and being competitive, as I'm not really a good thrower and have a inaccurate over arm throw so in the heat of the moment i will always under arm throw. I didn't mind doing exercise classes and fitness tests or any running activity. Unfortunately, my school loves doing unfair matches in sports and will always play a game of rounders or football. Can someone help me? I don't know what to do?