Concerned about dress sizing

My dress at the bridal shop fit with a little wiggle room and clamped with may a few inches to spare. This was a size 12 and they ordered me a size 8 as they suggested this would fit perfectly. Well today I went to try on veils and the 12 barely fits due to a slight increase in glute size. I've reviewed the sizing chart for my designer and my hips have never been what a size 8 suggests and my bust far surpasses a size 8 and in fact puts me in a size 14. I am concerned on what I should do. The shop was less than friendly and told me to loose weight. My God I am a size 6, not sure what they expect. I am wondering if I should buy another dress with only 5 months to spare or pray to god I loose 5 inches in my butt alone. What would you do?