How do I change the output size of the camera?

I am making a game where the right 1/4th of the screen is being used for a 2d UI overlay. However, when I use the 3d camera, it outputs to the size of my entire layout. Is there a way to shrink the output so that the camera is outputting only into a certain area, so that my UI doesn't cover up so much of the 3d area?

For anyone who had this problem, I fixed it by messing with the horizontal vanishing point % on my layout properties, and moving it to the left so that it 'centered' there instead of on my UI.