Ugh, been there, done that! Uni student here, and I still do that.
I have a little tip for myself - 'if I doesn't matter in a year, it doesn't matter now'.
I struggle quite a lot with body issues and the way I look. A good friend told me once that people are too caught up worried about themselves - how they look, what they're doing - to worry about the things you're doing.
I struggled a lot at sixth form, especially with friends stuff - try and break down the day. I even do it at work sometimes. Think, 'I've just got through 5 minutes, I can do the next 5, then the next 5 etc'
You've so got this!