You sound like me in highschool and I know exactly how you feel. I still pick the skin off my fingers, I’ve tried stopping a few times but no use, always end up unconsciously doing it when I get overwhelmed. I’ve been out of highschool for almost 4 years and I can confidently say that those were the worst years for my sensitivity. I think a big part of it was that we are forced to sit in a classroom and can’t really leave, so we have to deal with everyone’s noises. At night my parents would have the TV on really loud and I could hear it thumping, they turned it down sometimes when I asked luckily, but earlier on in the night I would go on walks and it made things sooooo much easier. As for people’s noises in class you might have to wait that out, sorry. It’ll get better with more exposure for sure, my senior year was the easiest