Firstly, as you know, the Tre Flip consists of using your back foot to scoop and flip while your front foot coordinates the slide off of the board in the right position. So if your back foot isn't kicking horizontally enough, you will not get the full 360 rotation. To get the full rotation, try kicking like you would kick off to push a scooter forward. If you aren't getting enough flip, then the problem could be your front slide foot or the direction of your back foot's kick on the board. You should be kicking slightly downwards and backwards with your back foot. Your foot's position on the back of the board should be almost like grabbing the edge that starts the curve of the board closest to your toe. This should give you more leverage on the down force of your kick and enough friction on the kickback. The front sliding foot should be angled to the outside of the board about 45 degrees and should slide along that plane. This will create the pressure differential on the board that will flip the board without stopping the turn. The video I'm including as a link below is really good for showing the motion of the front and back feet, as well as the position of your feet for the ideal, not so sketchy, Tre Flip.
Hope this helps.
https://www.youtube.com/watch?v=QuOcEBS8Qfk
