This is a sample apology letter for a Misunderstanding.
I realize that we have had a bit of a misunderstanding regarding favor shown by you to ………………… (Person Name). I am sorry for contributing to this misunderstanding. I just misunderstood your notion of generosity and so the things went wrong. With a little patience on my part, this whole mess could have been avoided.
I am very sorry if I have hurt your feelings or caused you undue stress over this situation. I hope that you will forgive me. We should learn a lesson from this incident and try to prevent occurrence of similar problems in future.
Please accept my sincere apologies.