I notice most when backing up. My boat seems to want to back up diagonally at best rather than a reverse arc
This may be caused from the tourque of the motor causing the boat stern to slip sideways. If you give a short burst of power to get the water moving past the lower unit to act as a rudder. Help overcome the side slip of the prop rotating May help you out? Or put dual counter rotating motors on.

. Thats a joke...unless your rich...
I drove a 30' CG Boat with a single screw and very small rudder. Had a Detriot 6V92T in it. With all the torque and small rudder it would also back up diagonally. Very hard to back into the slip.