1) You need to edge progressively into the wake. You're coming off your edge before the wake which is not right. You want to build your edge more and more as you approach the wake and be at maximum edge at the top of the wake. If you reach your max edge capability before you hit the top of the wake then you did it wrong. Right now in your video you are edging your hardest before you even hit the white wash, then you let off on your edge through the trough. The backroll is a load and release trick, so you need to build your line tension and release it off the top of the wake. Right now you're releasing your tension half way to the wake and have none left at the top of the wake.
2) Edge in and hit the wake in a taller position. Lean against the line to build your edge and don't bend your knees very much at all for this trick.
3) Why are you doing a frontside 180 slide before all your attempts? Just take a normal toeside edge out and heelside edge in until you have this trick consistent. No need to over complicate things.