just got this trick, but never had this problem a good thing to note would be not to pop super hard otherwise it could be a jerky motion and would make the spin uncomfortable.
The absolute biggest thing that helped me learn this trick is to keep your head up while sliding on the box or rail. So normally with a front 270 off you would keep your eyes on the landing the whole time scissor your feet and then pop to spin and your head staring at the landing would counteract your spin to stop it at 270. So try at keep your eyes and head looking at the end or a little above the end of the box as apposed to the landing or looking down at your skis which you may be doing without even realizing.
Pop onto the feature, keep your head up and looking at the end of the feature not at your skis as you get to the end wind up your back arm a little bit, start to scissor your skis whilst throwing your arm that you wound up around and pop. Keep your HEAD UP, it will help let your spin continue. Thats what i do at least and thats what works for me.