You have to imagine that your clew is mast and mast is your clew, close mast and control power with clew. It is harder, yes, you need to add straight more than normal waterstart. It helps me when I image that sides of sail is changed. Use your bodywaight to close sail.

put your sail in downwind to start, this s more easy

Head more downwind when you are un the water, the sail will be more stable and the rest is just a normal waterstart

Try waterstarting facing more downwind ..and as you get on the board keep your body low for control dont get up to fast you will lose control..

I think you need more practice clew-first riding, and you get control in this sail position! Good luck !)

try practicing switch more. then try this water start clew first again and see that your balance will improve. it doesn't come as easy as regular so you gotta feel the balance first to get used to it

Hold the boom wider, try to start more downwind. All the way keep your sail fully powered by pulling mast hand. Dont lean the sail too much upwind, only downwind! Orient the board downwind by pulling back leg closer to you

More downwind help a lot. To train put yourself in a normal water start position and just feel the sail. Then rotate the board to the other direction with your feet, keeping the sail in the same position/direction and feel the sail again. While getting up push down the boom toward the board with the mast hand.

You should use sail to sand up and control the power of the wind.