A Letter Of Resignation

Thank you very much for your offer of a promising job with your company. However, it is unfortunate that I feel that I am not competent enough for it. Consequently, I have made the difficult decision to resign.
It has been two years since I arrived here. Never did I imagine that I would leave your company. Some of the reasons I must leave are;  not having enough working experience and professional skill, such as in writing, and speaking.  It would not be practical for me nor beneficial for your company if I continue in this position. I feel that I lack the necessary positive attitudes and working enthusiasm.
I ask that you would honor my request and please accept my apology for any inconvenience that I may have caused. Thank you 
Yours sincerely
Li Ming