Gallery width and organisation with Snapshot Plus and NextGEN Gallery

I have tryed NextGEN Gallery and experimented some issues to get the result I expected:

1/ I would like the gallery to use all the screen width (allready chosen the “full with” page mode)
2/ and I would like the gallery to be well organized in columns an lines

Can anyone help?

Here is the picture of what I want to do: https://www.lgphotography.fr/Help/Fauna

And here is the page I am working on: https://www.lgphotography.fr/wordpress/fauna/

I am using Snapshot Theme https://siteorigin.com/theme/snapshot/ with Snapshot Plus Extension.

Thank you!!!

https://www.ads-software.com/plugins/nextgen-gallery/