Jetpack Tiled Gallery Full width/Fill screen

I’m using a child theme of 2012. I have my wrappers, content divs etc all fluid and set to 100% width.

I would like to create a tiled gallery that fills the screen. Currently, while my page text fills the screen, the gallery stops at 960px.

I’ve not been able to find any thread where 100% width is addressed, even just to prove it can’t be done.

I’ve seen plenty of threads that end in “Just set your content_width…” but I don’t think that will help me, as I’m not dealing in fixed widths.

My Content_width is defined at 1200px just to see if that did anything and it doesn’t.

Any help would be greatly appreciated!