Mask is showing background frame border

I'm a novice at masking in Premiere, but have been messing around with a personal project to try and learn different effects.

I was able to create the effect I wanted using 2 masks on this image to get rid of the background, but when I moved the position and zoomed the masked image out, I noticed that the original frame lines are visible for some reason? Can anyone help me figure out why? Thanks!