David`s Bridal Slip 603 Size 12

I bought this slip for $50 for my wedding dress, i was told i needed it. My dress is the da vinci 8008 and it seems like there is a slip built in already unlike the davids dress i tried on at the store. When i got home and tried it with my dress that i ordered online i looked like a bell, and relized that the slip is not returnable! Still in the package, brand new with tags on it, i tried it on the one time. The slip gives a little lift, it is the least puffy one. Any questions feel free to email me. Looking to sell it for $40 or best offer.