If the wing tip to rudder measurement is off it's going to cause a "yaw" effect on the airplane. Especially if you have dihedral. 3/8 of an inch is most likely not going to cause a noticable problem, but keep in mind that's what going on when your wing is not "square". If you have dihedral then any yaw will lead to a roll. So be careful to adjust the right control surface when trimming out the aircraft.