Wide hips big butt

My birthday dinner is tomorrow and I bought a tight dress that hugs the curves. I’m not 100% confident in it tbh as I tried it on again and just want to cry. My hips are super wide but I’m very frail and skinny every where else. My butt is nowhere to be found, it’s as flat as a board. so from the back my butt looks square and flat bc of the wide hips. I bought the skims shapewear and it helps a little bit but damn…. I just don’t know if I could go out like this and feel good about it…