Replying to Front 450 help????

Lately I have been trying front 4s on my backyard setup but I come across a reoccurring problem. For the most part I get the 4 spin around but as I pass 270 my body slowly drifts off axis (btw I slide left foot forward). By the time I get around my back is on the ground. I try to keep my head as level as possible but it doesn't help. This seems like this happens a lot with this trick and people landing backseat. Any tips on how to avoid this problem would be very helpful, thanks!