Two things I noticed on your backhand side.
1) You want to bend your right knee prior to contact a little more. Having a stiff leg like that prevents you from being able to fully rotate.
2) You seem to be a bit off balance after hitting your shot. Try bringing your left foot around and having both your left and right feet pointing towards the net once you complete your rotation after contact. You came closest to doing this on the backhand you hit at 0:58. Your balance also happened to be greatest on that shot.