Thanks for reaching out. Could you try clearing your browser's cache and cookies or use different browser and Incognito mode? Let us know if this helps clear things up.
To clarify, in the "Get a custom URL" box, you'll see the custom URL(s) you've been approved for. You can't change the part in the gray box, but you may need to add a few letters or numbers to make the URL unique to you. More info here: https://goo.gl/YQKMnU