i think that is a dealer problem and they have fobbed you off, the lens is not fitted square properly, or been jolted?
I reverse the Jazz into the garage and used a laser measure to mark the exact centre of the door gap at the back of the garage with a white board and vertical red tape. When I reverse in I know I have around 30cm spare each side of the car (with the mirrors in) so keep that distance on the driver side, head out of open window. If I manage to stop perfectly square then the marker is exacty in the middle of the yellow box on screen.
Likewise the E has self parking where there are good white lines. If I set to self park it ends up exactly in the middle of the white lines and the screen yellow box is central to position.