How much actual gap is there? All the hole really does is locate the back plate in the right place so it's centered when you tighten it down. It does absolutely nothing once you've torqued the prop nut down. So if we're just talking about a slight rattle it won't hurt a thing to center it as best you can and put the prop on. The worst case scenario is that you'll be 1/32 off center which doubtfully means more off balance than a plastic spinner already is from the factory due to manufacturing tolerances. Your plane will never know the difference once it's all tightened down.