How do you write letter for urgent piece of work?

To,
The Principal
OPF Public School
X Y Z
R/Madam
With due respect i beg to say that I have an urgent piece of work at my home.So,Icannot attend the School to day.Kindly grant me leave for 2 days.
I shall be very thank ful to you.

Yours obediently
X Y Z
Date 15-4-2013 Class 9th