Yeah, I think it's a length issue. Aren't those dresses supposed to just barely cover the rear? It seems long to me, for a slut dress, that is...
So if it is intended for someone taller, would those side panels on your thighs hit up higher, on your waist, and the curve then would help to suck in the tummy? I'm guessing those side curves are intended to do *something*... maybe carve out a waist?
Are you petite? At 5', I have this issue with all sorts of similar items, including spanx, exercise gear, and negiligees. Oh, and even underwear. Underwear fits goofy on me.
I vote "it's not your body, it's the dress."
You could try saving it by altering it from below the bodice. What would happen if you chopped off about 6 inches at the top of the black part, and moved it all up?