Personally, I'd let it ride and taste it before messing with it, but you can add sugar or DME or anything else that's fermentable to the beer at pretty much any time.
The Fiesty(sic) Goat Brewery est. 2007 & Clusterfuggle Experimental Ales est. 2009
Planned: sLambic II, Flanders Red II
Primary: Saison, Berliner Weisse, Dark Mild, sLambic I
Secondary: Orange Blossom Mead, Flanders Red I
Kegged: Fat Man Porter w/ 1469, Fat Man Porter w/ 005, Centennial Falcon w/ Conan, Centennial Falcon w/ Denny's, Barrel-aged Fat Man Porter, Belgian Dark Strong
Bottled: Flanders Red I