Wedding gown with boning, size small?

If ihad to guess, i would say this is a size 4. My dress form is a size 6 and i couldn't zip it up on the last inch. Needs to be dry-cleaned. See pics. In pretty good condition expect for one dirt mark on side, towards bottom and one discoloration of one applique on back bottom. No tags whatsoever. Not sure of the fabric. Beading seems to be in tact- but i havent looked closely at all the Beading on the dress either. Measurements were taken while garment was flat: Waist: 16 inches flat Pit to pit is 16 inches retro romantic wedding festival rave date night cocktail party modest sexy Holiday Christmas Fitted Classic Cinderella Ball gown Beading Princess Beautiful