If you really care that much about your performance, then maybe run more??? Being upset because you didn't run well after not training to run well makes no sense. That's like me going out to the golf course (I never golf) and being mad that I don't par every hole.
Figure out why you like or used to like races. If it's because you like being competitive then you should train more to be competitive. If it's because you like the atmosphere and the comradery of everyone out there at the same time, then stop caring about the performance and just focus on the experience.