I responded by noting that I had apologized, and that I had forgotten about the email trail, and if there was a better reply, please inform me. How else could I have replied?
MERYL RESPONDS: His response sounds scolding and parental, and the natural reaction to accusation is to get defensive. What if you started by telling him he was right instead? What could you have sincerely followed that up with? ..
If I were the manager, unless it was a huge error or you had history of doing this, "oops" would be appropriate. For him it wasn't. He needed something else. You might have said,
You're right. Oops might suggest that I don't take what happened seriously. I do. I regret my error and it won't happen again.