For future reference, hitting PrtScn and then opening Paint and hitting CTRL+V will produce a better screenshot without monitor glares and all that ;p
as for your issue, try right-clicking the scene object containing the gameplay -> Position/Size -> Fit to Screen
If that doesn't fill the ENTIRE stream, you could try going into its properties to see if it has a Stretch Image to Screen/Ignore Aspect Ratio tickbox and mess with those (though I wouldn't try to stretch the image just to achieve full-screen or whatever)