That happened for me. They gave me the call with the first offer and I accepted, knowing I had other offers pending but not thinking I'd get any of them. Two days later I got the call for the second offer and they were super nice about it. They congratulated me and then said if I wanted to cancel the first offer it wouldn't look bad on me at all. I was told all the details of both and given a day or two to think about it. I ended up going with the first offer, but it was comforting to know I was allowed to change my mind if I wanted. Without wanting to sound like a snob, it's apparently VERY rare that people get offered two. Good luck to you!!