Just stop. The end.
No need to explain why you didn't do something, and honestly, most people don't even care why.
Just apologize, sincerely, and move on.
This isn't an ADHD issue, it's a maturing thing. Many people rationalize their mistakes while apologizing, which just devalues the apology.
Own the mistake, apologize for it, and move on. By doing this, you show respect and consideration for those you've affected, while also freeing yourself from the justification/rationalization feedback loop in your head.