For one, as per Psych Central, you should accept that you can’t change the past. What’s done was done. But we can learn from it. So stop thinking I should have or I shouldn’t have. It’s not going to help. Be proactive about the situation and apologize, or make-up for the inappropriate behavior in a timely manner, but then let it go.  Obsessing about it, without any compensatory behavior, only feeds the hungry guilt monster.