Remember that for every 'mistake' or bad experience, there is something to learn. So ask yourself what lesson you can learn from the experience and add it to your wisdom. Your life experiences are valuable and it is wisdom that cannot be earned in any other way. Things happen for a reason.. if you don't take the valuable lesson from it, then the chance is that you are doomed to repeat it until you do learn the lesson.
There's many things that have happened to me which were unpleasant but when I'm on the other side of it I can see what I've learned. So I encourage you to look for the positive from the situation, no matter how insignificant it may seem. It could be something like 'I learned that I need to tune my guitar before a gig' or 'at least I now know that I shouldn't do
that...'
Try writing a list. Write down your negative feelings about the gig.. get it all out. Then do a second list of the positive things that resulted from it. If you look, there will be good things that you can take from it.. but you do have to look. It's human nature to wallow in the negative but the positive side is always there, in plain site.. we just have to look for it.