Justify width

Dear developer and users,

I'm developing a little website and I've recently been using the plug-in Post Grid. The plug-in is truly fantastic, I'm almost 100% satisfied!  The only problem is that I would like to keep the alignment of the posts symmetric (justified) with the alignment of the rest of my homepage. I would like to stretch the posts across the width so that 1. each post has an equal width and 2. the posts take up the full boxed width of the page. I've created this as an example: https://imgur.com/a/1bGhr. Is there any way to achieve this?

Kind regards,

Jansen