I believe RC Ken has posted something, (perhaps a link??) as to the steps to follow when making adjustments to control surfaces like that. These are procedures that are followed step by step to adjust out any yaw and roll tendencies caused by mechanical adjustments not being optimal for that particular aircraft.

Simply centering the surfaces is not the answer because of other factors that will cause the airplane to fly with some roll or yaw tendencies even though the surfaces are centered. This will require some trim adjustment followed by mechanical adjustments to remove the trim adjustments you just made.. but I don't exactly recall what the procedure is. Perhaps RC Ken can post the link, if in fact he is the one that originally posted it, and since he is the "all-knowing guru" here he can probably point you in the right direction.

DS.