If the stepper motor chops, add a washer, sheet metal piece or similar. It can be made of plastic. The purpose is for the switch to turn on before the stepper motor tries to tear off the film.

Try the winding on wheels - c. Both starting position winds up in the center and simulates full roll with 2 pieces of tape.

 

The wheel in the picture is a maximum of 120 meters / 5 inches for this scanner