What may help for you (has helped for me):
Work the motions while standing on flat ground. Make sure you understand the posture and technique right down to the gut level. Then go onto a gentle slope and do the move while concentrating on the technique and not on what's happening to you and your board.
This sounds like trite advice to "just do it right", but it isn't. You are unconsciously reacting in some way to the turn and the slope and (probably) leaning back. So instead, go into the turn motion and concentrate on holding your weight on your forward foot and holding your shoulders rotated heelside. Forget about the board and the slope, forget about avoiding a crash. Forget about your goal being to complete the turn. Make your goal to keep your weight on your forward foot for a few seconds longer. Be a statue. Your technique will probably suck, but you very likely will complete the turn.