500 error

Help please! I have managed to crash my localhost site and can’t figure out why or how to fix it. I was in my wp admin panel, in settings. There are two fields there with site URLs. They both had my site URL (localhost/devljwood). Since I have been experiencing my site not opening to the home page, but to a 404 page, I decided to try changing the URL in these settings (yes, stupid, I know, to try changing something I didn’t really understand). I changed them both to localhost/devljwood/home and when I clicked save, I got the following:

“The server encountered an internal error or misconfiguration and was unable to complete your request. Please contact the server administrator, you@example.com and inform them of the time the error occurred, and anything you might have done that may have caused the error. More information about this error may be available in the server error log.”

When I changed them back and clicked save again, I got the same error message. Now cannot get back into my wp admin at all. I only get the error.

I realize this is probably not a theme-related question, but I hope you can help! I am using MAMP if that’s relevant.

Thank you!
Leslye