英语翻译Dear Mr.X,It is really a hard decision for me to tender

英语翻译
Dear Mr.X,
It is really a hard decision for me to tender this designation to quit my position as secretary in the company with effective date from (the last date) because ("由于我自身能力的不足,近期的工作让我觉得力不从心"或者"同时在曾经的工作当中,我也曾模糊的意识到自己学识的浅薄.虽然十分热爱自己的事业,确又隐约觉得力不从心")
Thank you for giving me a chance to learn and to gain the valuable experience in (company name and section work with).I hope my resignation would not cause you much inconvenience.
Thank you for your kind attention and would appreciate if you could let me have a reference letter before I leave.
Yours faithfully,