Jersey material does need particular care when being cleaned, and we give specific instructions on the website and the garment tag; these include not placing in a hot wash, nor using a dryer. You may find that you are able to bring some stretch back into the fabric by ironing it on a warm iron and gently re-shaping it.
If this does not work, please submit a ticket using the “Returns & Exchanges option” and our customer care specialists will try to rectify the situation to your satisfaction.