remove the woodruff key and clean out the slot area for it.
then put it in, if its a tight fit, you might need to tap it gently down with a hammer or something. Sometimes, they will not go down and seat all the way.
I like to take a marker and mark on the end of the crank shaft the same spot / placement. that is inline with the wodo ruff. this also helps when I line it up to slide on the flywheel.
Sporty