Robert Pattinson has said his sex scene with Kristen Stewart was "scary". In an interview with Britain's Reveal magazine - the 25-year-old actor talks about the raunchy scene he had with his girlfriend on the set of The Twilight Saga: Breaking Dawn - Part 1. He explained, "I've never done a sex scene where it's kind of scary because you think something is going to fall on you! There was a whole…