Using the Ellipse Mask within Lumetri Color creates unwanted Black Bars on the sides of my video.

I am trying to highlight a certain part of my frame by lowering the exposure of the entire image except for a certain area by using an inverted ellipse mask - but when I click the ellipse mask, it cuts off a large chunk of both sides of the frame. 

My only work around is stack the clip on top of itself and then crop the edges to get the image from the sides back, but i would really like to know why this is happening. 

Photos attached.