No I usually forget too.

For ailerons or tail surfaces I use two straight popscicle sticks (or something equally straight) and lay one on the top of the aileron (chordwise) overlaping the wing and one on the bottom of the aileron (still chordwise) overlaping the bottom. Then use a clothes pin or something similar to spring load them in place. You can see the stick become tangent to the gap between the surface and touch it equally on either side.

Put one every foot or so across the surface with a minimum of two per surface. It pretty well automatically centers the movable part with respect to the fixed part. It will also hold it firmly enough to use the incidence meters on the whole wing/surface.