I hope this letter finds you well. I am writing to apologize for my forgetfulness. I know that I have let you down and I am truly sorry for that.
I understand that my forgetfulness has caused you some inconvenience and I want to make it up to you. I know that I have not been as reliable as I should have been and I regret that. I have been trying to be more organized and mindful of my commitments, but I realize that I have still been falling short.
I am determined to do better. I have taken steps to make sure that I am more organized and that I am better able to keep track of my commitments. I am also making sure to set reminders for myself and to double check my calendar to make sure that I don't forget any important tasks.
I understand that this may not make up for the inconvenience that I have caused you, but I want you to know that I am taking steps to ensure that this does not happen again. I am sorry for my forgetfulness and I hope that you can forgive me.