Customize Image Gallery in WebsiteBuilder

I am trying to customize an image gallery in WebsiteBuilder.  For example, when I go to Elements and select Images - Image Gallery - Grid, it brings up a two column gallery.  What I would like is a 3 column gallery with perfectly square spaces.  I know it will revert to square, or whatever format I have my images in but I don't like cropped preview or thumbnail images.

How might I go about this?  Please remember that tho I am a longtime SiteBuilder user, I am still a newbie in WebsiteBuilder and I need beginner level instructions!
Thanks!