I didn't. But I do feel similar now. Everyone knows I'll do well, everyone knows damn well I'll emerge with four As, couple of STEP papers, and trot off happily to Cambridge. Everyone except me.
However, year 11 is nothing, trust me. Your GCSEs are important, but (as long as you prepare for them correctly, and aren't terrible in any subjects) they're absolutely piss easy. A-levels are the difficult exams. Only thing is, most people don't know how to prepare for GCSEs properly, because even teachers give you stupid explanations on how to prepare for them (because, let's be honest, teachers often took their GCSEs or O-levels many many years ago and have forgotten entirely what it was like, and things have changed, and they think that if you can't remember that x = [-b ± root(b^2 - 4ac)] / 2a, there's something wrong with you
). Even if you find them difficult because you're underprepared, or badly prepared, GCSEs aren't the end of the world. There's always the possibility of resits if you really cock up, and if you don't and get a few A*s and/or As under your belt, you'll be fine.
Leaving sixth form / college sounds like it might be good for you - an assumption this may be from what you said, but I don't think you really like your friends.
In the end, things may be going quickly for you, but they're going quickly for everyone. Enjoy the time you have left and in the end, whether you want to go or not, you'll be ready to leave school and hopefully go to university.