Put the washers on the blade, and insert the bushing. They will 'stick' to the blade because of the oil.
Then align the blade/washers/bushing with the handles
and start inserting it into the handles. At first you might think that it doesn't fit, but it SHOULD fit! If it doesn't fit, you assembled it wrong, see message from Chris Reeve at the top.
You need to hold the blade in such a way that you keep the bushing in place with your thumb and fore-finger and then slide it between the handles.
Do not unscrew the stop-pin screw to make room. It should and will fit!