Need help removing washing machine pump inlet cover

I have a whirlpool and I cant get the new chopper installed!!! I get it in there, BUT it doesnt lock into the impeller, even with maneuvering. Also when I rotate it, I can tell one blade is scraping against plastic on the bottom. Probably hard to see, but I cannot for the life of me get that white part to engage with the impeller. I have the screen in the right slot, perhaps did the place give me the wrong chopper?

http://i.imgur.com/e8HC1.jpg