Need a tweak on my backroll.

I have tried the backroll at least 50 times and although I have plenty of height, have a nice slow rotation, and am landing on the board, I get crushed on the landings. I have watched my video in slow motion and I am keeping the rope tight to my hip. I have noticed that the board sometimes lands a little sideways but not always. I am definitely landing flat on the board - that may be my problem. Seems as though my knees are getting driven up through my shoulders. I am using a 65 foot non-stretch rope at a speed of 22-23. I know I am close to finally stomping this mother - I think I just need a tweak. Thanks.