Probably just more time on the water needed. The main things to remember:

Leaning back with weight on your heels is key

Try to stay "locked" at the hips and keep leaning back, letting your board dig in like a brake rather than getting pulled forward from your waist

SLOW DOWN, bar out and control your momentum (can't emphasise enough)

Don't have your kite too high in the window, this will lift your weight making it difficult to edge, sit the kite around 10.30 / 1.30

Blatant pimp here .............
Buy a Shinn - theres nothing that compares for upwind.