Prevent the screen from stretching in different resolutions

I've experimented with the new UI system of unity and, while everything scales and looks really neatly, I ran into one problem: I've tested build on two monitors both with different physical aspect ratios. My monitors' aspect ratio is 1.5, yet running the build on the lowest resolution it is 1.(3). For some reason my monitor stretches the screen to fill the entire screen space, therefore the x axis and all sprites are stretched. Is there a way to add pillars to the sides or letterboxes so the aspect ratio would be "real" and not stretched to fill space? C#.

Thank you in advance, it's 5 a.m. and I'm crashing into the bed.