Did you actually manage to upload the image to WikiTree? (It won't work unless it is on this site, and while I see you have uploaded images for primary profile pictures, I haven't found where you uploaded anything that looks to me like a background image.)
If it is uploaded here, Did you upload it to your own profile, or some other profile/page?
What is the image? (Do you have a link to it?)
Did you click to set it as background?
Have you tried to add it as background to any other profile/s?