I don't cosplay but I do suffer from that same sense of acute anxiety. It can be a bear to cope with at times and I'm guessing it comes from a sense of being a perfectionist. Am I right?
The best advice I can give for that is simple... stop being so hard on yourself. People are cruel... they do judge... and they'll do whatever it takes to get ahead. You know what though? No amount of worry, fear, or predicting what will happen will change any of that. Go out there and be the best you can be and at the end of the day if that's not good enough for your friends, family, or anybody else then forget them.
Chances are that all of the worries will slip away once you get out there though. Cosplayers get so much love and love melts away all anxiety (among a ton of other things that ail us human beings).