You say you are finishing up this wing but a bit more info would help.  What exactly do you mean by uncovered?  Bellcrank, leadouts, leadout guide installed?

FWIW, my built-up Brodak Legacy, 690-ish square inches, flaps & control system installed but otherwise waiting for covering is 16 ounces even.  Given that foam wings are supposed to be a bit heavier than built-up (but ignoring the fact that I tend to build heavy), you don't seem to be too far off the mark.