I am sure that site will help, but it looks like the trigger is out of position. There is a little point on the back of the trigger than has to go below, not above the bottom of the trigger housing. Put the hammer pin in first, then the hammer spring and housing, then hold the whole thing sort of like a pistol with your index finger pulling the back of the trigger (keep that point below the housing) and you should be able to drop the trigger pin in.
Jim