Form size now suddenly TOO SMALL

Hello all. Im not sure what ive done wrong now lol.  But my forum is now tiny. I was deleting a bunch of posts from a thread. And I noticed while I was doing that, my forum (on screen) was getting smaller. It is now still small, and I cant figure out how to make it bigger, or if it has effected the way others see it.

Here is the forum in question http://mosinitus.americantalk.net/

I realize this may be hard to understand. So I will try to post pictures.

Here is a picture of this forum. It appears normal size.


Now here is a picture of my forum. It has shrunk in size.

you will notice in the second image, the right and left edges of the forum do not touch the edge of the screen. Where as, they actually used to.

Ok, i have managed to restore it back to normal size. But still unsure what I did to cause it to shrink.