I think it's only 88' wide. (only...haha) 

But yeah, either test it by driving one way on your line and back on the same line the other way and see if the tractor itself and GPS settings are good. Then put planter in the ground and do the same thing...on the same line. That will narrow down if it's a tractor/gps/steering issue or if it's only when you have planter down it's dragging to one side.