This can be filed in our "emotional illusions" file.
Without knowing the details, I would hazard to guess that 1) it wasn't nearly as bad as you think it was, and 2) the worst part of it was probably self-fulfilling, that is, you thinking you are a bad guest made you a less-good guest.
It was a big step for you to go solo to a party. That's no easy thing, especially for abuse survivors with social anxiety. I wouldn't have done well there, either, I don't think.
So pat yourself on the back, and send whoever invited you a thank-you note saying you had a great time but had to leave early because of either a) another stop you had to make or b) because you weren't feeling 100%.
RIP Bryan, Life's A Dream, LAD, my little brother. I will not forget you.