There's really only one way to attach the selector disk to the selector lever. If you look closely at the other side (the side that is facing down on the table in the first pic) you'll see a semi-circle/dome indent on the disk. That should match up with the stub on the selector lever. Basically, if the arm of the lever is down (semi-auto position), the disk is up. In your third pic, the disk is pretty much in semi-auto position...the lever should be pointed down.
If the stub on the selector lever doesn't fit nicely into the indent...you're going to have a wonky selector. The fit should be tight, but not that you need much force to push the two together (you'll strip the screw hole or split the lip of the indent if you force it).
When tightened up...the selector should move relatively easily from position to position. If not, check that the rim of the disk/indent is a good fit to the hole in the body (I've had a few that weren't really round and would bind in the hole).