Size 4 BNWT Wedding Dress

Here's the thing. This is the most ridiculous situation to have ended up in: I bought the EXACT same dress as my sister in law to be. To marry her husband's brother. At the same venue they got married at. And I thought I could be cool with it but turns out I can't be. Brand new, unworn, unaltered, with tags wedding dress. Straight from the bridal shop to my closet, in a bag! Gorgeous dress (with pockets!!) with lovely beading. It fit very well everywhere except the shoulders being too long, meaning it would be perfect for someone larger chested, too. I'm usually a 6-8, and it's a size 4. It has a horsehair hem, and is standard length. The inner layer of tulle has sparkle in it, and it shows through really nicely. It is super light and airy, perfect for a summer wedding. It's a little off white, but definitely more white than cream or nude. I bought it on sale for $800, and I'd just like what most of what I paid for it back, since I'm now planning on buying a new dress. Measurements: waist 29 in bust 35 in shoulder to waist 16 in