I don't do side to side marking with a gizmo, only down the center. I do draw a zigzag pencil line across the gizmo mark side to side on the limb to be sure I take wood off evenly.
My advise is mark a center line with your gizmo, get your bow bending correctly, if the string is off center as you close in on final poundage work the strong side of the limbs to center it. It sounds like you are getting too much information from your gizmo that may take you off into space with your tillering.