An apology to my boss

I have to write an apology e-mail to my boss and I would like that you help me with it. My boss works in Weybridge (UK), so my apology must be in English.

"Dear Mr. Shemilt:

I would like to apologize for delaying the development of the last BMW model. This model was assigned to me with two weeks of advance because I only had to update it. Normally for updating a BMW model we use need two weeks, but for developing a new BMW model we need four weeks or aproximately a month. It is was suppossed that the BMW Serie 5 was an simple update, but while I was developing it I saw that is not true.

BMW Serie 5 was developed in Bratislava office in 2011 and the rules in that year do not exist now, so I had to do the update like a new model.

I tried to develop the model as fast as I could but it was impossible to me although of I worked hard for three weeks.

If you need more information about this subject, you can call me and I could tell you more about it.  explain it to you very well.

Best Regards.

David"

Very good! - I could understand all that you meant even without corrections.