Guests at Prada’s swanky party to show off the luxury line’s costumes for “The Great Gatsby” this week had trouble standing in their stilettos on the SoHo flagship’s slick floors. A spy reports, “The floor curves; there are stairs and ledges. You’d be talking to someone and move an inch, and stumble because you couldn’t tell where the floor changed. Two women fell hard. They kept the celebrities on flat ground.” A rep for Prada tell us this is “not accurate.” Katy Perry, Catherine Martin and Baz Luhrmann attended.