Free People Lavender Smocked Sweetheart Strapless Skater Dress

Large Free People lavender strapless skater mini dress with smocked bodice and sweetheart neckline. Purple roses, yellow leaves and burgundy flowers and polka dots on bodice. Worn one time. There’s a dark spot on the back that looks like it just might be dirt, I have no idea what it is or how it got there since this dress has been only worn once and it was such a long time ago. I haven’t tried to get it out. Feel free to ask any questions.