How important is the placement of the keyway on a propeller – not knowing your circumstance, keyway and key are rather critical to holding propellers onto tapered shafts. If the key is sloppy in the keyway, movement of the propeller could back off the nuts, or stress the shaft to a breaking point. Keyways in propellers should be cut in under a blade.
Proper keyway would have radiused corners, and the key would be file fit to it.