There isn't always a tomorrow. Make tomorrow today.
Be who you are. Don't be like others. Let you shine into the world and let people be awed by your brand of awesome.
Learn from it, remember the lesson, forget the details of what happened, and move on. Do not let it torture you or others as it will just hold you back. Don't let it hold you back.
Saying you are sorry and wrong is not regret. It is not trying to undo the past. It is simply admitting you were wrong - admitting you have grown enough to say you are sorry for being the person you are not proud you were who you were when you did what you did. Improvement is not regret. Do not let too long pass until you admit that to yourself and to those you have hurt.