Hindsight is, in fact, 20/20 and while it may seem like a good idea to just move forward and leave the past where it is when you have a revelation that you've wronged someone, returning to that person and apologizing is probably an even better idea.
There will be times in life when you have to apologize to someone you can’t stand and with whom you do not agree on anything, but for somebody else’s sake. For example, you may need to apologize to your stepparent, when you did nothing wrong, just because having you two fight is breaking your biological parent’s heart.
If we all just started lashing out because we felt we deserved it because of our bad days then the world would be a horrifying place. Part of being a well-adjusted adult and good member of society is containing your pain and struggles to yourself rather than lashing out at others around you.
So you messed up, but it's not too late to make it right.
Do the words "I'm sorry" get stuck in your throat?