You sound like you are hurting a good deal over this. For this I am sorry.
You are not cursed and it is not possible to be over a bad (wrong) action and it is NOT impossible to let it go.
You are holding onto this for a reason. Sometimes when we do things that we know are wrong we like to punish ourselves a bit before we get to the matter of realizing we aren’t perfect and need to work on letting it go.

You hurt because you really like this girl and wish you had not gone against your better judgment and tried to impress the guys.
You knew it was wrong but did it anyway and this is the shame and guilt you are feeling.
You weren’t true to yourself and what you know is right.

We all mess up, fall short, get driven by things and we all feel this sorrow that you are feeling.

First of all:
Do not repeat to yourself that it is IMPOSSIBLE to let this go!
You are empowering the negative by doing this.

As a man thinks so is he.

Began thinking along other lines such as that you are human, made a mistake, see the wrong and want to improve and not do it again.

You have learned a valuable lesson early on that will help you immensely for the rest of your life.

The lesson is:

Be true to yourself!
Forgive yourself!
Learn from your mistakes and move on!

I wish you well!