i am not sure if the letter from embassy will satisfy uscis's request.  you need to get a letter from your wada office from the town you live in back home.  i think it's called "panjikadhikari ko karyalaya" or something (i am sure i messed up the spelling on that one but i am sure someone back home will know aobut it).  they will have a standard template for providing birth certifications and it will be in nepali which will have the government stamp on it.  it needs to be translated into english and notarized.  you need to send a copy of both the original and translated copy to the uscis which will satisfy uscis's request.

just make sure that it has both your parents name as well as the place of birth.  usually they only put the fathers name on these certifications. hope this helps.