We make a lot of mistakes in our life, but there's really no use in letting them burden us for the rest of our life.
Some people are hung up on their old regrets to the point where they may in fact make some new ones.
The past is in the past for a reason. We are going to have to move on and just learn a lesson. Understand that if you spent time being hung up on old regrets, we won't have much of a present or future.
No matter how much we wish things could be different, we can't change the past. Which might be a good thing as we might end up doing something that could cause even greater damage if we could.
Do what you can in the present, that's the time we have now.