Notice that two of the corners are "pointed", and one has a small flat. There is only one way it will go together. Match the flat with the flat and it should go.
Like supraman said, index it the right way and it will go. Pour some type of oil on it to help and get them in the same plane of level. I would say remove the plastic crap that is useless but the safety nazis will scream bloody murder.
I had a hell of a time the first time I was trying to put a pto shaft together. Friend of mine came to the rescue to show me the flat bit. Felt like a complete idiot when he had it together in 2 seconds.