I tried to change my domain on my site to greatwallgiftshop .com in Cpanel, and when I did so it said this
*You have successfully created the new “greatwallgiftshop.com” domain with the document root of “/home1/nnlffnte/public_html”.*
I can no longer edit my site. When I click the button to it sends me to this greatwallgiftshop .com filler site. How do I unlink this domain and try again? Is it lost?
You need to make sure the new domain has the correct host records, and is pointing to your web server. Then make sure you changed the site URL on WordPress, either through the database or by adding it to your wp-config.php
Looks like your domain has expired and been purchased by someone else.
Check your site files to confirm the domain is pointing correctly, and remember to update the home and site URL as well.
Check the wp-config.php and also check your database for the site url.
Since the domain you mentioned is currently taking you to a placeholder page by Network Solutions, that means that you do not have your domain set to point to your hosting.
Also, you should edit your post to remove username, as once the domain is pointing to correct server, hackers have one piece of the puzzle to attempt to log into your hosting account, just need to guess the password.