Wow, bad luck. It looks like it should be painful.
Gybing overpowered in choppy water is much like bottom turning on waves here in the uk

. It's really important to engage the rail so that you slice through the chop and make your turn more predictable. Here's a few tips to help you do this.
Move your back hand right down the boom before you initiate the turn. The extra leverage will help you control the power in the rig.
As you start turning, lean the rig into the turn and oversheet, pulling your back hand almost behind you. This does three things. It dumps the power in the rig so that it's easier to turn the board off the rail, it puts pressure on your back foot which engages the rail and it directs the power from your rig (through the mast base) sideways into the water keeping the nose from bouncing around.
Don't hold the over-sheeted position too long, perhaps a second at most. It'll help you turn faster and tighter so you'll need to open the rig faster too. Once the rail is engaged you'll have the control (hopefully) to open the rig and move it forwards.
Remember to ensure that your back foot is as far back as possible to engage the rail. Banking the board over on the soft rail further up the board is less effective and you'll be more likely to trip.
So, wide hands, wide feet and oversheet. Easy (not)

Good luck