Who did you tell? My DS and I have different last names, legally I never changed mine but I'd like to use his last name which the name I use except for taxes and travel.
As you walk on the ship, they just ask you and you can tell them any name you like - Brad Pitt and family; the Teddy Rooseveldt family, the Happy family. I've been quite impressed that they don't seem to mangle the names too badly.
Nancy