Honestly I'm sorry your going through this, its so hard when its your hands because of how much you use them so are onstantly seeing them and remindedof them.I use fingerless gloves and try to make sure I pick the hand I dont write with so covering it with fingerless gloves if possible but with the hot weather I've found the thing that works best for me is thumbholsleeves there like tights material so not the thickest or most protective but can cover the scars and also help take your mind off it by covering (but you shouldnt feel and pressure to hide what hlped you cope.) I just bought some off Amazon but you can get them pretty much anywhere online or maybe DIY with some tights. I put the pen through the thumbhole with my thumb so the pen rest against my skin if that makes sense. Sorry because this might not help if it's your fingers you struggle with but for me it's the back of my hands getting scratched thats the problem. It's not gross or embarrassing dont worry if your worried about infection wash thoroughly with soap and water cover with a fin layer of germolene(or another gentle antiseptic clean) and keep covered until the skin has healed over changing the covering at least every 12 hours. I know it's not easy but if you haven't try telling someone in school they would be able to give you firs aid if needed. Other times simply writing no on my hand helps but it's about having a variety or coping tools at hand. If the urge is to destroy then allow yourself time away from studying to safely scribble or rip paper sort of thing, I hope this helps and good luck with your exams.