the width being set for the gallery needs to be increased by 20 pixels.
in the /pGallery/galleries/ribbon_fullsize_lightbox/js/gallery.js file, find the following line
$$('.pg-rfl').setStyle('width', fullSize.getSize().x + navPrev.getSize().x + navNext.getSize().x);
and change it to:
$$('.pg-rfl').setStyle('width', fullSize.getSize().x + navPrev.getSize().x + navNext.getSize().x + 20);