Have you got it yet mate? If not try this. When you are in the trackstand position with your strong foot forward and ready to go squat your body down with your arms straight and back slightly curved forward. Then in one movement push down with your strong foot and pull your arms half of your arms lenght towards your body and jumping up straighing your body. It needs to be a snapy movement. If you are going back and not forward its because your standing up too high with your arms too close to your body. Also try practicing this without your bike.
Sry if this makes no sens as its the first time iv described the technique. Good luck