Done something stupid ! can't login

I have just done something very stupid while trying to tweek the website.

I went into the “editor” in “appearance” and changed “www.watermill-crafts.com/blog (blog being the name of the directory where wordpress is located) to http://www.watermill-crafts.com.

I now can’t get back into the admin area of wordpress to change this back and can’t establish which wordpress file has been changed.

I’ve spent several hours without success so any help would be really appreciated.