Real Event OCD (TRIGGER WARNING)

So when I was younger I wanna say between 12-15 (there’s no way for me to be sure, to clarify I am 21 now), I made a mistake. I was at someone’s house watching a movie and their little sister was always close with me and when we were watching she cuddled up with me and it was fine. At some point my hand was like between her thighs and I can’t remember but I feel like I thought about it or may have moved my hand closer to her private area and I just can’t seem to remember how far or if I did or what and it is honestly killing me now. At the time I was aware what I was doing, but I didn’t know how that could hurt or effect someone. Nothing changed after the event to indicate she was uncomfortable or anything but I feel so guilty as if I took advantage of a situation despite my age and lack of understanding of the seriousness. Recent events in my life brought up the memory and I can’t help but to feel terrible and I replay that memory every 5 minutes in my mind wishing it never happened and feeling like a sick awful person. I want to accept what I did and forgive myself but also recognize it was wrong. I know this is a little on the stronger more questionable side of things, and I don’t want anyone to subject anyone to this but I honestly don’t know where else to go. I am trying to pursue clarity or at least self forgiveness for an event that probably happened 8 years ago, but am currently struggling. To all I hope you all can find clarity in what you’re going through, and find a way out of OCD controlling your life.