Correct, the sheet is the underlining. You could sew it together via the interlining seams but I'm going to treat it more as an appliqué, tucking the interlining seams underneath and mounting each panel separately to a twill under bodice. The seams will be covered with beads or sequins, not sure what yet.
I'm doing it this way in case I need to alter or repair the bodice at some point. Also it's much easier to do this method of beading with the tension of a hoop and by keeping the panels small it makes it much easier to have that. :>