Corset vintage 50s style maxi swing (fit and flare) sleeveless dress

I bought this dress from a shop on Etsy; ZynabeClothing, this shop no longer sells on Etsy. it's beautiful, but the only issue is there are built-in in cups that are too small for me, I think they'd fit a (b-c, maybe d). there is a zipper and corset closure. waist is 14 inches length of dress is 40 inches it's brand new. It didn't have tags attached.