The sooner and franker... the better.

I've spent countless hours kicking myself for stupid things I've done. However I've also figured out that learning how to recover from those mistakes is key. For instance knowing how to apologize is incredibly important. A simple acknowledgment that you messed up goes a long way. There is no need for long speeches and explanations. Just say "I didn't handle that very well. I apologize."

The sooner you do this after recognizing your mistake, the better. If you wait a long time to apologize, the damage continues to grow.