From what I see, you sit a little too much on your bum, you should be more on the front of your seat than so much back.
Look where you are going, not where the horses head is, eg, lift your head and look further out.
your upper body looks a bit stiff, like you are trying a bit too hard, i would say shorten the reigns a bit, loosen your arms, then shoulders and relax all the way through. I know, easy to say, I sometimes have the same issue, but with lots of work one can loosen up and be with the horse :)
in the video it looked like you are trying to cramp on the reigns into your stomach.
It is not all bad, you ride well, its just there is always something to improve..