Kicker kicker kicker.... MAINSHEET TENSION.... then cunningham. Seriously, never underestimate the amount of kicker which you need. Then once you have enough of that on and you are overpowered then start going to town on the cunningham to loosen up the top of the sail. As Matt says, without seeing photos it is difficult to tell, but in around 95% of photos, people always look like they could do with more kicker with these big square tops.
Make sure you are keeping the boom on or near the centreline to give you height. If you are spilling too much wind to stay upright then you might want to rake the rig a bit more too, so that you can keep the main sheeted sufficiently. Might be worth checking mainsheet strop lengths to make sure you have got the boom in the middle before you get block to block.
Otherwise, swing it flat and work it in the gusts to maximise your height. Don't pinch though, as that is slow and the boat will stall out.
