ImagelessRocket yes that is your current Windows Size. make sure nothing is selected(click on blank space in layout view in unsure) then on the lefthand side(properties window) it says Project Properties click view. Under project setting there is a Windows Size setting change that to what you want that dotted line to be
I recommend looking though the manual it helps you learn C2 easier.
https://www.scirra.com/manual/36/interface