I am writing to apologize for my unintentional omission in [describe the situation]. I am deeply sorry for not fulfilling my obligations.
It was never my intention to cause any disruption or distress to you or anyone else. I understand that I have failed to meet my responsibilities, and I regret my actions.
I understand that my omission has caused a great deal of inconvenience to you and your team, and I can only imagine how frustrated you must have felt. I am truly sorry for not being able to meet my obligations.
I take full responsibility for my actions and I am willing to make up for it in any way I can. I am willing to work extra hours and put in extra effort to make up for the lost time and effort.
I understand that this is not enough to make up for my mistake, but I hope that it will show you my commitment to rectifying the situation.
Once again, I apologize for my unintentional omission and I hope that you can find it in your heart to forgive me.