XS Rainbow Peacock Full length Tailored formal dress (Prom etc) fully lined

I looove this dress but I bought it JUST before I stared lifting at the gym & now my muscles won’t zip in!! It’s 2nd hand, super tiny with a side zipper. Is full length, strapless with a sweet heart neckline. Flexi corset boning with sewn in boob cups 14” PTP laid flat 12” at the waist … tiny tiny 51” long -From the high point of the bust to floor