Main Page Background MIA

You’ll need to contact WordPress.com’s support: https://en.support.wordpresss.com

It sounds like you’re referring to the featured image on the latest posts. Looks like you added another post with a large featured image, which is displaying as it should, so perhaps you’re all set.

As Andrew mentioned above, these forums are for folks running the WordPress software on their own hosting, not on WordPress.com. If you need further help with your theme on WordPress.com, feel free to post in the themes forum here:
https://en.forums.wordpress.com/forum/themes

Here are some tips on getting help in the WordPress.com forums: https://en.support.wordpress.com/getting-help-in-the-forums/

You can also access the live chat support option when available here:

https://wordpress.com/help/contact