We all make mistakes, some large, some not so large. We can minimize them, downplay them, and deny them. But they are always there. Who we are is defined by how we handle mistakes.
Do we ask for fogiveness? Say we regret the mistake? Say I am sorry? What truly needs to happen is to change place mentally with the person you offended and find out what hurts the most. Then go and address these issues quickly and with sincerity. If they forgive you great but if not then let it and them go.
This is truly about letting it go and forgiving yourself. Its easier to ask forgiveness than to forgive. This is true in our external and internal interactions. The internal is far harder. We relive moments, see the pain we cause and know we must do better. Some among us possess a grace that allows them to realize their humanity and move on. Some of us never see the pain we cause and are oblivious. Some know the pain they cause and enjoy inflicting it. And then some know and see the pain they cause and want to make it better. It is to the latter group that this message falls.
First, realize your shortcomings. Certain people,places, and things create negative situations for us. Avoid them all. Do whatever it takes. Cause no harm but make the change to avoid having to bear the scars later. Second, the mistake happens and you make it right with the other person. Third, allow yourself the anger, the shame, the disappointment. Then work on getting better. Be especially nice to strangers and nicer to your friends. Go out of your way for others. Then go and he nice to yourself. You allow yourself forgiveness when you believe you deserve it. And not before.
That is all you can do. Give yourself time to fix it. Life takes time.