No confidence...

I have to go swimming with a group from school as a team building exercise (we go to Germany next summer) and I'm reaaaaaaaly dreading it. They are ALL popular and skinny and I know I'm gonna be left out but I don't wanna be left out looking so fat. I recent put on 30lbs and it all went to my stomach. Before I had a little cellulite but now it's everywhere. No 16 y/o girl has so much cellulite. And I have old self harm scars on my thigh that a friend has already seen from wearing this swim suit. I use fake tan lotion to try to cover them up but it only goes so far. Can you help build me up or give tips for self love and confidence?