Hmmm. That sounds odd. If you are not touching the sticks it shouldn't be doing that. If there is a little bit of yaw that is occurring it could be accumulated error throughout the flight. This is something in the DJI flight controller that cannot be fixed by us. The fix is to the bottom of the Settings screen and enable Advanced Settings. Then select Straight Corners. This will make it so it does a full stop at the corners. This slows down the flight but it resets the yaw for every pass.