I have read your post several times, and I just don't understand why you feel so guilty.
You were 12. She was 9.
You kissed a couple of times.
What's the harm?
Am I missing something?
Were you tongue-kissing a 9 year old? Is that why you feel guilty?
Or were you touching her sexually while you were kissing her?
It sounds to me like you were both kids having a normal childhood sexual experience.
Heck, I bet that girl isn't anywhere near as bothered about this as you are. In fact, this probably was a positive experience for her.