Goood luck Tensed Bro, I truly understand ur feeling at this point. Though you are in PHD level and I am in udergrad. I went to Nepal in Dec and visa had expired. I went to renew and at one point of interview I had regreted my self why I went cause the Counsellor(lady) was rude at the time of interview and I was thinking at the point what I would do if she denied me. As I had only one Quarter, i.e 10 weeks was remaining to graduate, I would have been truly in trouble if I was denied as it took me 6 years to be at that point. Lucky that I had just a Bank statement of 5000$ of Bof A. I was been asked several Hw and Wh questions but was granted though.

Goood luck bro ..  . . just be cool and face the interview.. . dont get mad at them or be polite, its we who wannnna something from them.