Are you riding powder or groomers? If not pow, why are you setting back your bindings? You're taking weight off the front of the board from doing that, hence why it's flapping. That's something that powder riders do to compensate for using a board not specifically built for powder, as it helps stop the nose dipping into the snow, and means you don't have to constantly keep as much weight on your tail.
You are also using a very short board for your weight. This sacrifices a lot of stability. I'd only put you on a 153 if you were riding park all day.