I am writing you this letter to show my deep regret.
I hope the chance will not cause too much trouble.
Please allow me to say sorry again, and I will try to make up for my fault.
Once again,I am sorry for my oversight.
Please forgive me and I assure you that such a matter will never happen again.
I'd like to express my great appreciation for your timely help and support.
Undoubtedly,it was your encouragement and support that cheered me up when I was faced with difficulties in English learning.
3.Nothing will be able to erase our wonderful memories.Thanks again for your help, and I'm sincerely looking forward to showing you around in order to repay your kindness.