the collet is what secures the crank to the inner race of the front bearing. Make sure the crank is all the way forward and the collet is seated against the inner race of the front bearing when you tighten the flywheel nut. There should be very little or no end play once the flywheel is tightened.

Use a small tuning screwdriver to wedge the slit in the collet slightly, it will slide on easily when done this way.