Distributor cap won't go on. Shaft seems too tall to fit rotor on underneath cap...

Frustrated. The cap won't go back on or it goes on, but it's seesawing on the rotor and this isn't how it's supposed to be. The shaft seems too tall or something. The distributor is already out. I can put the cap on without the rotor in place, but it won't go on with the rotor under the cap. Yes, the rotor is fitted in properly with the notch on the distributor shaft and everything, so it's not that. Would appreciate the help.