If you're willing to consider failed suicide to get help, perhaps it is a sign that you should just get help before you scare your loved ones. I know what you're thinking and have thought the same thing myself, but those kind of fantasies are dangerous. As for gym, have you ever seen those compression shorts for athletes? Try slipping on a set under your gym shorts that don't show (at least much) but are tight and won't reveal scars. If anyone asks, say they make you feel more comfortable and since they are athletic gear, no one will make you stop wearing them. (That is, if the scars are on your legs, arms and I couldn't find a solution for that either).
You need to find out what part of school it is that stresses you so much so that you can address it as soon as possible. Stay strong and try to be positive. If you need support, feel free to
PM me!