My belt hangs about 3mm off the edge of the rear sprocket both going forward and in reverse.
The best way I have found on my car to align the belt is to jack the back end up so the rear wheel is just off the ground, remove the boot liner slacken the axle nut just enough so it can move in the swing arm forks with a little force. Then slacken off the adjuster lock nuts.
Use the adjuster bolts to align the wheel so the belt tracks in the same place whilst rotating the wheel forwards and backwards. The belt will find its own best place, mine has always been about 3mm off the edge of the pulley. Tighten the adjuster lock nuts and then the axle nut. That should do it.
What makes me think yours is out of true is the witness mark on the bevel box pulley. It should only be the width of the belt, yours is much wider than the belt which would suggest the belt is wandering from side to side.
Hope this helps.
