That sounds so stressful! Do you have anyone in your group who you feel safe with? It's good you talked to the prof about it already. I wouldn't try and tough it out... Why make yourself do something that will cause such stress and possibly lead to a panic? Life is too short and what will it prove? Do you have ideas about where you could go (like a safety plan) if things get too much to handle?

Maybe bring some comfort object with you? Lots of calming things like a scent that calms you (peppermint, lavendar - unless they are triggering for some reason), or something you can keep on you? Maybe it sounds superstitious but I do things like that. If I'm nervous for a job interview I'll use a little lavendar balm and wear a specific necklace.

What kind of class is it? I'd have such a hard time sleeping in a big room of that many people and with all the classes, mixed genders, etc. It would be way too over-stimulating... I would not feel any peace or ease, just lots of anxiety.. So it sounds like a really challenging situation. You have my support if you decide to go or if you don't, either way it will work out ok for you I hope.