Installation screw-up

I’m new at this, and seem to have created a problem I can’t resolve. I created a blog site in WordPress, and it was going fine, until I tried to change the connecting URL to eliminate the need for “/blog”. The problem is that when I did that another site popped up. So, I slightly modified the URL to deal with that, but now when I try to open it I get a “Page not found” message. Except that the blog title and picture I uploaded are right there, followed by the “This is embarrassing, isn’t it” message. I can’t access the site to fix it because the URL no longer works.

What do I do to repair this mess I’ve created?