After you killed the southeast golem and moved south, you got the southwest golem positioned perfectly for a kill - and then you didn't kill it! Why not?
Other general advice is you may want to randomly drop a bunch of trapdoors towards the middle, just to create more places for the remaining golems to get stuck so you can position them where you want.
If all else fails, you can watch Dolan42's demo
here to see how to trap golems in the corners. Kill two or three of the golems on the bomb blast spots, and then use the corner trick for whatever's left.