Something not quite right here, like the pinion not in the right place on the shaft, mainshaft not passing through the bearing as it should, a plain washer that is too thick, or a kickstart ratchet inner bush slightly too long. All assuming they are the right parts to start with.
Have a look at recent posts showing the correct location of the mainshaft pinion on the shaft, make sure the shaft with pinion is seated next to the inner race using a spacer tube and the nut to draw it through. Don't use the soft bush, it will bell out. Having said that the shaft should be just a push fit through the race with just a light tap to assist. The mainshaft needs to come out to check the pinion has been pushed on up to the circlip. The nut should go well onto the thread with room for a tab washer as well.
Swarfy