Ubuntu – Changed hostname, closed before changing hosts, now sudo is broken, catch-22!

I'm using Lubuntu 12.04.

I was trying to change my computer name to "main" and I messed up, I'm not sure what to do now.

I was following the directions on this page.

Here's what I did:

sudo leafpad /etc/hostname

I changed the name, then stupidly closed the file, before changing "/etc/hosts"

Now when I try to move on to the next step (sudo leafpad /etc/hosts), or try any command that begins with "sudo" I get this error:

sudo: unable to resolve host main
No protocol specified
No protocol specified

I can see that the problem is that I've changed the hostname, so the computer's bewildered by my efforts to use sudo because now hostname and hosts don't match. All I need to do is change the name in hosts, but of course I can't do that without sudo.

Any ideas?