I can't judge well enough from the video, but I think the problem is in the grip. If you take a look at this picture http://www.google.nl/imgres?start=36...84,s:300,i:256
and take a look at the position of the thumb. The base of the thumb is on the index finger. If you do this, your angle between your racket and wrist will likely be more towards 90 degrees.