Hey,
Its good that you came here. Right up front I see three things that tell me you hurt, feel guilty and probably ashamed. You are trying to hide what you are doing, calling it bad and wrong. Are you sure that isn't what you are thinking about yourself? I know, psychobabble. Really though, you are a high achiever at a young age, and as good as that is, it also creates a lot of pressure for you. My guess is that people expect a lot from you, and even if you enjoy competition, and get good grades, you feel the pressure. You are probably good at controlling your anxiety at some level, otherwise you couldn't successfully compete at the level you are at, but sports and grades are not all there is to you.

Sometimes we spend so much time trying to live up to other people's expectations, that personal feelings are put aside or kept in a room behind a door that we try not to open. If you look around at the people in this section of the forum, they are intelligent, artistic and sensitive. Not all come from bad situations, though many do. Something is bothering you. It could be the pressure of always trying to be the best at what you do, or perhaps you have something bothering you and no one to talk to. I don't mean gripping about something with your friends, but rather things that are inside, personal and painful. SI usually gives people some sort of temporary relief from something. I don't think I'd call it wrong or bad. Its not an effective way of coping with emotional pain, but it doesn't make you a bad person.

Since you are using the term "mates", I'm guessing you are not from the US, and if that is true, I don't know what kind of health system or insurance you have where you are. You need to talk to someone though. I understand not wanting to have anyone find that you are cutting. People that don't understand it might turn away or think the cutter is weird. You aren't alone in that. I still have to come up with explainations for all the scars I have and feel like the people that notice them see right through the excuses. There are some good therapists that see cutters and won't judge you. Going to a therapist doesn't mean you are crazy, and since they have to keep it between you and him or her, you don't have to worry about it getting out. If you don't want your parents to know (God knows I didn't and they still don't!), you can tell them you feel a little stressed about competition and want to talk to someone about it.

Please don't beat yourself up about what you are doing. You are already punishing yourself. You aren't a bad person, or crazy or weak. You've just gotten stuck somewhere and need help getting out. My biggest worry is that you might inadvertantly cut too deep and either permanantly disable a limb or bleed out. It happens. If you aren't ready to go outside the forum for help, then come here when you feel like you might be in danger of cutting yourself. You don't want to look back ten years from now and think, "gee, I could have done something back then to stop myself" and still be cutting.
Let us know how you are doing.

Sam2