Keep that airlock full. As long as the flies don't get into the beer you are perfectly fine, bro. Most likely the flies got through the airlock cap.
And as anyone here will tell you - NEVER throw out a batch. Always let it age to term, and if it tastes off at that point, let it age some more - months even...
8-Paws Brewing Co.
Primary:.DFH Indian Brown Clone (10g)