I wish I had your depth of seat at sitting trot!
You look really relaxed and quiet which is always a good thing.
The only thing I have to say is that you seem to grip with your knee sometimes, and that's when your lower leg seems to become unstable and wobble around a bit. I do this a lot. Most of the time you were fine but there were a couple of points where you seemed to tense up, and therefore grip with the knee. I don't know if your horse is normally laid back like that, but your lower leg coming off her (due to you gripping with your knee instead) could've contributed to why she kept slowing in the trot and falling back to the walk?
One more thing.. sit tall, shoulders back, perky boobs