Plus size wedding dress

Bought this beautiful dress but I do not look good in it. It makes my boobs look way to big and doesn't hide my arms at all. I wear a street size 18. It's a corset back, tightened all the way. It's loose so it should fit a size 20 perfect, or do the alterations for a 14,16,18 Did not have alterations done yet. I am not wearing any body shaper underneath. It is light and easy to move around in. It's not itchy or uncomfortable at all. it has a satin lining inside. Selling for 350 with shipping. Still has tags.