You've got a choice here - feel bad, look backwards, beat yourself up about what you did; or look forwards, learn from the experience, feel positive about the future.
You can't change the past. You can change the future. So chin up, look forwards not back, change what you have the ability to change instead of dwelling on what's done, and what you can't change.
Don't panic, just put it behind you and keep your eye on the goal!