Background behind a rotated video segment not visible in playback

Newbie here, so this may be a simple fix - I found a tutorial about how to combine video shot in landscape and portrait, using transform and rotate. Since the resulting rotated portion of the video now presents the pillar boxes, the tutorial instructed to insert a background image (a jpeg) in a channel below the video to create a more visually pleasing video frame…I followed the instructions - and figured out how to change the length of the background image to match the length of the rotated video (the tutorial used “grab”, but that would not work to re-size, it only allowed me to “move” the image), but the background does not show up in playback. Thoughts? Screenshot linked below - image shows transparent pillar boxes and correct positioning of the background image. Many thanks in advance for any suggestions.