Did you linked single listing page from Directorist settings? if not then please link it from "Directory Settings >> Pages, Links & Views" and then access your single listing page like this URL "www.yourdomain.com/directory/listing-title".
If the page is already linked up but still not working, then please share us the page link of your single listing page.
Currently, there has some limitation on customizing the single listing page, but we are fixing it in upcoming updates by bringing a custom page template for the single listing page, where you can customize the single listing page in more flexible way.
Sceenshot below shows, where form the huge gap at the top is coming from:
By the way, you can fix it by placing the following CSS in Appearance >> Customize >> Additional CSS