How long are you staying in Nepal? Visa renewals can sometimes take 3-4 weeks (maybe even more) if the embassy is receiving large number of applications. It took 3 weeks for one of my friends to get his visa renewed last summer. First thing you want to do when you get to Nepal is pay the damn fee and get a date for the interview. I'm not sure about the specific documents you'll need though. Maybe your current and all past I-20s, undergrad diploma, letter of acceptance you got from your gradschool, etc. 

riddle, could you ask your friends what documents they had to show at the interview and share the info here?