It doesn't look like you are setting it hard enough. Really throw all your momentum up and back with your arms and then pull your legs up ASAP. Get somebody to double bounce you too. You simply need more height as well.
Here is a video of the first dub back I landed..
Courtesy of Newschoolers.com
Oh and one more thing I noticed... If you pause your second attempt in the video, you aren't looking back. Make sure your head is looking back as far as possible, it will speed up your rotation and you will start flipping earlier because you kind of pause in the air before you start your first flip.
Good luck brah