I'd call expedia and the airline and see if the can make a change somehow. The US can be really strict about names, I've been summoned while in the airport (flying from a US airport) because my middle name wasn't on my ticket (but is on my passport). They told me it flagged as a non matching name - fortunately with a few minutes of my time and a sensible supervisor it was resolved, but I can only imagine the problems a 'different' last name would cause, especially trying to enter the US (I was leaving to a country that really doesn't seem to mind middle names at all!)