Whenever I get a bad result in a comp, I just laugh at it and move on because there's really nothing you can do about it. Stressing about it will only make things worse. Also, be sure to socialize with other cubers! This is coming from an introvert, and it's something that is very hard for me to do, but every interaction I've had with a cuber in a competition was positive. Knowing that no one there is judging your bad solves (except for your judge lol) really boosts self confidence and results in better times.