I called someone a fatty

I am 28 now and was just reading my old Facebook messages from when I was in middle school and yikes I am so mortified and ashamed of myself. I’ve always been a quiet nice girl, but this one case particularly this boy really liked me and didn’t want to let me go, so I was just so mean to him. I said “goodbye fatty” and taunted him and stuff. He also said some not nice things to me too.. we were a little toxic but then in another case I blatantly lied about something very serious! I am just… how can I forgive myself for this? I feel like a fraud saying I’m a good person knowing I acted like that as a child! I feel disgusted in myself. I would NEVER do this as an adult. I just am so embarrassed that I did that to someone…