I Am Worried and Anxious

I never thought I'd say this...But I remember 1 year ago I had chatted with a girl either the same age or 1 year younger than me on here. I won't say what the picture we both sent were, but she had told me it would be okay (I was very unsure at the time) and that if she showed a picture of her then I would have to send one of myself (I hid my identity). But now at 18, I remember and realized something wasn't right about what we did. I've been looking for her on here to get in contact with her to tell her what we did was a mistake. But I can't find "M". So I have no clue what to do, I won't search anymore for now since there's more important stuff for me to finish. But it does suddenly hit me and get me anxious and worried at weird times. I just hope "M" messages me or I find her and message.