Help!

When I was editing my website, I went into "Advanced settings" and edited the your site url and i accedentaly deleted some of it so I typed http://mywebsite.com/social but I was supposed to type http://mywebsite.com/social/... When I tried to go to the links it was like http://mywebsite.com/socialactivity. Then the next time I went on, I was logged out and when I tried to log in it did /socialaction/login and when I add the / it brings me back to the login. How can I fix this?