You might also try afjusting the centering of the brake by loosening the back nut adjusting to center and tightening it back up,that screw is supposed to be a micro adjust for brake pad width only.Also check if yer brake cable housing is too short as this will cause the caliper to come out of alignment over time.
if it has a nice smooth curve from bar to brake its ok, if it comes out of the bar tape at an acute angle(perhaps you raised the stem ) it will be too short .