I think I may just have either the wrong prop adapter or wrong propeller.

Starting with the adapter shaft, I slide the tapered backplate on. Next, I put the spinner backplate through followed by the propeller. Then I put the washer on. The last thing is the nut, but there isn't enough room to even begin tightening it down.

The propeller seems to have a pretty thick center section, should this be thinner?

An alternative way that I tried to attach it is:
Slide the adapter backplate onto the adapter shaft. Put the spinner backplate on, put the washer on and use the nut to screw this down. Place the prop in the spinner top (it's very tight), then try and screw this onto the spinner backplate. Going this route, there isn't enough room between the prop and the adapter nut to actually get the spinner on to the backplate assembly.

So, which part should I replace?

Thanks!