Can't get rid of white line in Rise lesson header

Hi, I hope someone can help with this. I have a Rise lesson I just started, and in previous lessons I created a graphic to go under the lesson header and to use throughout as a dividing block. I have the same color on the header background and it is supposed to seamlessly blend in as with other Rise courses I have made - but for some reason I can't get rid of the white line. I have tried every thing - resizing the graphic, cropping, trying different lesson headers, publishing it in Review to see if it was just a preview glitch. I just can't get rid of it. Please help!

Update: I went back and changed the theme and that fixed it. Apparently it is a glitch in the Rise theme because it did not show in the Horizon theme. I am not sure there is anything that can be fixed if that is the case unless a developer looks into it.