Remove white line from covers in fliphtml5 flipbook

Hi, I’m making a fliphtml5 flipbook using a magazine design I made in InDesign then transferred to Adobe Express. (I can’t work in InDesign at this time). Once I created the flipbook, it has a thin white line on the right-hand side of the front cover and on the left side of the back cover. (Both covers have a black background so it’s noticeable). Is it possible to remove the white line? Below is how the far right side of the front cover looks.