Sounds like your all out of balance there busta.
Firstly, don't worry about the straps much if your not planing.
As far as the harness goes, it sounds like its too far forward if it's trimming out the sail. Basically if your hooked in and let go of the boom the end of the boom you feel the need to grab first is the direction you need to move your lines. The ideal spot is when powered up the boom can be let go and stay in balance a while, even a tad further back is Ok.
Don't try and use the furthest back footstrap positions until your use to sailing powered up, go for the more user friendly - forward and inboard options if they exist.
When your planing well and hooked in, lean out square to the board not aft and rake the mast further aft, it may all come together in balance
