Pilotfighter hit the nail on the head with his answer.

Yes, the spinner DOES need to be tight against the backplate. If you start the engine without it tight you are risking the entire assembly coming apart and causing injury or damage to persons or property in the area. But the solution is pretty simple. Just cut a little bit off of the center bolt used to mount the spinner. Take off a little bit at a time until you can tighten the spinner all the down to the backplate.

Ken