thumbnails displaying in half width

Hi, great plugin!

I have a questions, in the screenshots the thumbnails are displayed the full width of the page, however on my page only take up half the width. this causes a problem as some of the galleries have a large amount of photos and this doubles the rows of thumbnails, and also wastes space to the right of it.

Can you help?

Thanks

Mark

https://wordpress.org/plugins/jsj-gallery-slideshow/