Site Totally Messed Up and WP Install Gone ?

Hi ,I was about to follow the “Moving WordPress Within Your Site”

I changed my URL from

https://www.mysite.com/blog

to

https://www.mysite.com/ just out of curiosity and saved it and had a look at my homepage and now my host says
404 Error File Not Found
The page you are looking for might have been removed,
had its name changed, or is temporarily unavailable.

Yep ,it had it’s name changed and now their text on the the homepage without CSS and skin and I cannot click links into subpages

Is there any easy way to get my site back or have I made a major mistake by changing my wordpress install URL to my main homepage ?

HEEEEEEEEEEEEEEELP !