If it's what I think it is,
Click on the display capture and than click on the actual image (in the part actually showing what you are recording). If it's registered that you've clicked on it, it should make a red border around the image. From there You should be able to either drag the image across the screen and center it,click on one of the red lines and use that to center it or be able to right click on it (Which brings up a menu) click on transform and click stretch to screen or fit on screen (One of the two)
If this is what I think it is this should work, although we may be talking about two different things lol.