Basically, no. Beer yeast can only eat certain kinds of sugars in wort. And once they've exhausted their food supply, they can't ferment any more and they settle to the bottom of the fermenter. What kind of sugars they eat & how much they eat is dependent on the yeast strain, the wort and the fermentation.
The one time you might 'over ferment' is if your beer gets a wild yeast infection. Wild yeast can eat more types of sugars than brewer's yeast.
But don't worry about wild yeasts right now. A cloudy beer after 8 days is not a big deal. It will probably clarify over time. It might not ever be crystal clear -- because home brewers don't filter or centrifuge their beers like many commercial brewers -- but it will still taste fine.