Custom aspect ratio/frame size exporting out of Resolve

I am editing a video ad intended for use on mobile social media, and we want an aspect ratio of about 1.1 so it is more eye-catching than a wider frame would be. I shot the ad in standard 1920x1080 HD. I did an initial edit in FCP X just to get the clips in place then exported to DaVinci Resolve 11 in the same resolution/ratio. I want to complete the project in Resolve and export directly out of it in 1190x1080 resolution, and the program seems to have functionality that should allow me to do this but when I try, The resulting export places my cropped image in a much larger black frame that seems to be preserving the original 1920 width. Any ideas as to what I am doing wrong or how to fix this?