The background image does not show up on preview

Just before I am making my form public, when I enter preview mode, I am no longer viewing the background that I entered with a url.  I can see it when I am building the form, but not in a preview.

The issue was related to your form's cache. 

I have cleared it for you from our end, so now the background should show up. 

I'll leave here a link about clearing form cache from your account:

How-to-Clear-Your-Form-Cache

Let us know if you need further assistance.