Apologizing to them is also enough to forgive yourself. Regardless if they won't accept the apology, you've grown enough to recognize past mistakes, and made reasonable attempts to amend them, there's no need to dwell on it any longer. It's okay to try and make the past right, and move forward with what You've learned and continue to grow as a person.
Even if the AI didn't train itself on actual CSAM that is something that feels inherently wrong. Your mind is not right to think that's acceptable IMO.