I'm rolling on the floor laughing, I think my small intestine is worming itself up my esophagus. *Cough* Anyways, you could have gotten something awesome but didn't, the chance was part of the fun.
So what? I've been plagued with thought most of my life, overthinking is such a pain. Stop thinking and act, or don't act at all. Thinking too much hurts. Stop caring.
Then what's the harm in playing your game? They did the most of their judging the moment they saw you, which I assume is a long time ago. This isn't going to make them loathe you even more.
After the presentations you'll feel better. Either it won't be nearly as bad as you're expecting or it will be bad but at least it will be over. I think you're overthinking it. It's okay if it sucks.
I didn't think I did well writing it and performing it was even more nervewracking, but overall I got a 67/70. I think you might be playing yourself down - you created whatever it is with your hands, a creative mind and some sh1tty markers. Own it :)
I actually had something like this happen today. We were supposed to perform our slam poems in front of the whole class but mine wasn't even finished 20 minutes before the presentations.
Artists always see their art as something-not-quite-right, you had a vision in your head of something amazing, I'm sure, but realistically it's difficult to achieve something like that. It's okay if it's dumb, it's a whole step forward.