8&3/4 axle shortening Q

Are you sure both pieces of the thrust button are in there? Were they pinned together?

Is it possible one side fell out when you put the center in?

You can check by pulling the axle out and look down the tube with a flashlight. If you see a "hole", it may have fallen out if they weren't pinned together.

I wouldn't like that kinda play, lack of bearing preload on that side will likely become an issue.