Thanks for taking the time to reach out to others. We know it can make you really nervous and uncomfortable when somebody sees the cuts on your arms, but your volleyball coach really had reason to be concerned about seeing those. Cutting is a really risky and dangerous way to cope with your feelings and problems. Since you're cutting we can imagine how strong and overwhelming your feelings are for you, and we are so sorry to hear that.
Your volleyball coach seeing your cuts might not have been the worst thing to happen. You might not feel as though you should stop cutting, but it really would be the best thing for you to do since cutting is such a risky and unhealthy way to cope with your feelings. One of the best ways to overcome cutting is through social support, guidance, and comfort. Leaning on your volleyball coach, the school counselor, parents, and friends would all be amazing sources of support and comfort. Overcoming cutting is tough, but it took courage just to reach out with your question on here...you honestly do have the strength to get through this.
Check this website it. It provides you with links about information to help you through this and also gives you a way to contact crisis counselors through email or online chat, totally free of charge: http://www.yourlifeyourvoice.org
i say try to talk to her..do you think you can trust her??...just try it if it doesn't work ask her not to bring it up to anybody..I know this isn't very helpful but try,,,for yourself/safety!...FYI that's what happened to me at gym...gym is our last class every Monday and Friday and you don't have to re-change into your clothes so one day I didn't and accidentally didn't bring a long sleeve shirt or a sweat shirt so I had to wear a shirt sleeve shirt which was a disaster! Because everybody could see the cuts up and down my arm..thankfully I just kept my arms crossed and we didn't do much that day involving our hands/arms but somebody must've noticed because they told my mom and she had a long talk to me...it wasn't bad but I wish it wasn't her..anyway talk to an adult!!