The component parts are added to the prop shaft in this order: Prop drive collar (as supplied with engine), spinner back plate, spinner bushing, propeller, prop washer (supplied with engine), prop nut (supplied with engine) and finally the spinner cone. Is this the proper sequence?
Sounds right except the bushing part. On Dubro spinners this generally presses into the spinner back plate from the rear so that the spinner will work with various shaft sizes. Is that how you assembled it or did you slide the back plate on the shaft then the bushing?
Also, I see a lot of people who simply don't torque the prop nut enough. Don't be afraid to put a little force on it. Both the nut and the crank threads are hardened.
Finally, make sure the engine isn't hydro-locked from too much fuel.
I see you are just up the hill from me. Are you a a local club member? Even if you aren't, feel free to head down 41 and stop by. It looks like rain tomorrow but if it clears up, the Wednesday crowd should be out. I'll also likely be there flying on Friday and definitely on Saturday weather permitting. I'd be glad to take a look at it and I'm sure most of the other members would be too.