It's not uncommon for the bearings to be tight fit and need some slight pressure or cleaning up with fine emery paper.
Really the bearing ID shouldn't be less than the the shaft if anything fractionally more but I suspect this down to your measuring equipment. It's much harder to measure the ID than the OD without correct measuring device.!

I would just clean the shaft with solvent then lightly lube and try again. Maybe a little clean up of shaft with emery paper depending on surface finish.?
Chances are that's all that will be needed.
If you want to try the Shaft in freeze and bearings on Radiator/oven job then it will make it bit easier but be careful it's not too tight and binding when on. If it still won't go after this then don't force it because some things wrong.!!

Good luck.