tomh is correct,
Unfortunately you should re hang the drywall. The brown side is not tapered to facilitate a flush joint when finishing. The paper on the grey side wraps around to the back making the joint much stronger and keeping the paper from separating. . The brown side does not wrap around the edge of the drywall and can separate from the sheet resulting in a weak joint and possible separation or the paper from the gypsum core. In addition the grey side is generally smoother resulting in a better finish.