School has had a huge impact on my anxiety! Help!

I'm in a really awkward position right now, and I feel like I could break down at any given moment.

For the last 3 months, I've been suffering from anxiety attacks on a regular basis. Some have been much worse than others. Today, I finally went back to school, thinking it would be a fun experience.

Oh, how wrong I was. See, I started my A levels today. And I'm now convinced I've made a huge mistake. All throughout the day, I felt really really uncomfortable around everybody. I nearly had a panic attack during school! Now, I've already started being given assignments and stuff, and I already feel like I can't cope. Also, I've been given so much to deal with - new people, new classes, and a more realistic image of just how challenging A levels are going to be. I don't think I can cope! I've made a huge mistake!

I barely got the grades for my GCSE courses. And aside from the uncomfortable feeling that I was receiving throughout the whole day, I just couldn't seem to relax and enjoy this new experience. I felt like I shouldn't be there. Gut instinct perhaps?

Anyway, I'm now terrified about going back tomorrow. What do I do?