If you are underrotating you might be counteracting the roll with your legs.
The next time you try it, try kicking your legs back and tucking them in as you are throwing your head and shoulders into the roll. It might help to pretend you are rolling up and over your spreader bar.
You'll go around very fast if you really tuck your legs in fast, extend your legs to slow the roll and stick your landing.
If you are overrotating then you need to extend your legs and straigten you body sooner in order to slow your roll.
Keep your kite at 45 or lower to ensure the kite won't pull you upwards, or else it doesn't count. Bear off or just flatten your board out to draw the kite back into the power. Unhook and cut as hard upwind as you can, tensioning the lines and creating your pop. As you feel yourself getting really lit up, pop it out of the water, concentrating on getting your front leg high and really booting off the back. Throw your head towards the water and look at the sky, try to roll your knees over your head. Once your board is over your head you have made it, spot the landing and throw a big claim. It is actually way easier to do it unhooked because the upper body is what leads, not the legs. If you are struggling to get the pop you can try learning it off chop or maybe more powered. The more power and tension the lines build, the more explosive and high your pop will be.
Good luck with it, and if you still can't get it around, just keep trying to look a bit further and before you know it you'll be hitting the water. Grab it.