I had the exact same thing happen to me last week. One of the HR persons called out of the blue and asked me a few additional questions and I could barely get any words out and I was embarrassed beyond belief. I was blocking on every other word and I wasn't able to say the answers that I wanted to say because I _knew_ that I wouldn't be able to get the words out. But on Friday afternoon, they scheduled a second off-site interview and they offered me the position at the end!!! Just want to say: you got this! If you know that you're a good fit for the position, that'll shine through. :)