I'm afraid it's pretty common among avoidants. The overreacting, the overthinking.
I hear you very well.
I don't know but I overcame a bit this issue. Mainly, I did testing irrational thoughts in therapy and boosted my self-steem.
I think these are the keys.

Think in an objective way if you really did something unforgiven. Would you punish a person if (s)he had done the same as you?
Surely, the two questions are answered with a no.

Also consider that many forums have an ending list of rules. Did you read all? i didn't.