I suggest cutting the foam blank according to the desired overall planform and then drawing a centerline all the way around the perimeter. Then cut the blank into three pieces- trialing edge full span plus an inboard and outboard leading edge blanks and add the centerlines. Then hotwire all three blanks to desired airfoil. You can then easily include a spar between leading and trailing sections and probably should as you have lost the integrity of the LE and some of the sheeting across the airfoil discontinuity. If you cut well on the foam blank centerlines, then you should be able to assemble a core and shucks that are compatible for skinning. Slice the skin at the discontinuity and skin the way you would normally.
Hope that makes sense.
John