Scared about being anxious for the first time. PLEASE HELP.

Okay. So writing this post is very difficult for me to say. I'm just gonna shorten down the story of why I'm sure I have "extremely bad" anxiety.
So basically, I met this girl, I was 18 and she was 15. We met up, hung out, kissed and that was it.
Obviously we talked before meeting up as I knew her for about 2 months but we then both decided to meet up.
We don't talk anymore, we go our separate ways.
Now I want to make this part extremely clear:
This is what I'm most scared about. I have never had anxiety before nor had panic attacks. But then when I met up with her and then we both stopped talking, I'm getting more anxious and really really scared. Only because she might tell someone that a guy who was 17 kissed her when she was 15. And I'm not like "one of those." I am in no way interested in girls underage at all. I find it disgusting. So I'm scared that later on in life she might tell someone, police will find out and then I'd get in trouble and be labelled as this disgusting human. But I'm not. I'm a really happy guy and I am never rude or anything that's negative. I'm basically always happy...except from when I think about this whole situation. I think about it everyday. And it scares me. I'm even too scared to look up the laws of this to see if what I done was illegal. I didn't ask the girl for sex, in fact I told her I would never have sex or do sexual things with a girl who is underage. But it's just the kissing part that makes me scared. I'm 19 now so I've been feeling like this for a long time. So what can I do?
I would go to therapy, but I'm too scared to tell them about this story unless they like tell someone. I would tell my parents, but they'd then think I'm a bad person. Rarely, I'd feel suicidal about all of this because I'm that scared. It's just one mistake I made, and I so badly f**king regret it.
I would appreciate it so much if someone could help me out with this. Or even give some advise. Thank you