Using the hot glue or the epoxy, glue the mirror to the tip of the motor. Try and get it as close to the middle as you can to reduce vibrations.
Also try and get it as flat as possible by 'eyeballing' it. This should get it flat but not so flat that it won't make a circle with the beam.
Attach the big mirror to the motor with the potentiometer attached and the smaller mirror to the motor without it.