Have you tried raking the mast well forward? Do you have the fins straight down in the rear well only, pedals held together? Rear turbos should also help moving the pivot point back.
Weathervaning comes from stuff in the rear of the boat catching wind vs an underwater pivot point too far forward. More formally in the middle picture below the wind's center of effort is behind the water's center of lateral resistance. When your sail is let out there is also windvane effect from your sail pushing forward on one side.
Do you have any wind catching cargo that can be shifted way forward? Maybe you could make a jib for the front stay, or even restep the mast forward. Is it your body catching wind like the feathers of an arrow?