Hi, I also had the same problem.
It seems that the ultra wide screen is not really 1920 x 360. I solved it by setting it to 1920 x 1080 by editing lines 14, 15 and 170
13 # marquee resolution: change to suit your marquee screen
14 marquee_width = 1920
15 marquee_height = 1080
168 # path to image viewer executable & options
169 viewer = /usr/bin/fbv2
170 viewer_opts = --noinfo --enlarge --ignore-aspect {file}
Let me know if you solve at least partially
