Nick, can you do a whirly on the tramp? Before I even attempted them behind the boat I learned a regular whirly and whirly 5's on the tramp, I think this is the most important thing you can do before trying them behind the boat.
As far as what your doing wrong in the video... you need to focus on a couple of things which have been said over and over again in the whirly help threads. Your cut is definitely too aggressive, you need to concentrate on taking you tantrum straight up and wake to wake. Start you cut closer and try to think about squaring completely up at the wake and popping off your toes at the peak of the wake. If you look at your video the reason your not rotating at all is because your keeping your left arm extended towards the boat, when you initiate a whirly, you need to make sure you pop, then throw your left arm across your body towards your right shoulder in a "punching" motion. Another way of thinking of this...try to stick your left armpit in your face. At the same time look over your right shoulder and commit to the trick.