I do not imagine that the yeast would have a hard time with that small a beer. I think it is done and the high FG is due to the LME. Also, what temp did you mash at?
IMHO, pitching more yeast now will not likely help, especially the S-05. If you decide to pitch anything, I would recommend using a lager yeast - they can ferment more types of sugars than ale yeasts, so you might be able to get a few more points.