Predicting FG is a hard thing to do. Wort fermentability varies, and some extract is less fermentable than others, so the beer could just be done. Another factor that probably compounded the problem is the high OG. Unless you made a really big starter (see mrmalty.com) and aerated well, the yeast may have pooped out. I've never had much luck restarting a stuck fermentation, but others may have advice for that.