It's not something that is easy to forget. I don't know whether it's correct or not either. What I tend to do is simple accept it. It happens, such is life. I messed up one exam as well this semester, and thought it would be bad, but in the end it won't affect your life as much as you think. Look forwards, take this as an experience, such things happen in life, try not to worry about them, instead, let them make you stronger as a person. You can become stronger from this, I know that :)