Margins on uploaded images

Hi everybody,
All my uploaded images are cut on each side on the book (and a little bit on top and bottom).
I use A4 size, but even if I change the size, I have the same issue.
Is there any setting in order to avoid this ? I did not find anything in the parameters to be set.
Thanks a lot in advance.

https://wordpress.org/plugins/page-flip-image-gallery/