i did as you said
Xstore>Theme options > Woocommerce (shop) > single product builder > Enabled
dragged and dropped (sizing guide) into section 3 .. with Title and Price and Product Rating
and nothing showing.
and then i go to the (edit product) area and found Xstore Option > Single Layout > Size guide image .. i uploaded an image and then nothing also
notice, I installed a plugin for size chart and i deactivated it when I found xstore has already one