Adding ImageStim mask creates unwanted white border

Hi, I’ve created an ImageStim in the Psychopy Builder and added a ‘circle’ mask. Including this mask creates unwanted white borders on the left and right sides of the image. These borders do not appear when the mask parameter is set to “None.” I tried playing around with the interpolate parameter, as has been suggested in other threads, but this hasn’t solved my issue. Any suggestions? Thank you.