On our Joomla gallery
demo - we have layout "All in one" - you may select in only in Pro version of OrdaSoft Joomla gallery -
There we created 3 categories - and in every we added images - specific for that category.
so there one gallery with many categories in it.
But on your image look like you created 2 galleries - and add them to some page with help Short codes. - Yes - you also may do so - but if you need 3 galleries per row - your layout must have 3 cells in row. Best for create so layouts use some page builder or ordasoft joomla cck
In OrdaSoft Joomla gallery, in layout "All in one" - you may add so many categories as you need - BUT if you have a lot images in your gallery - please use gallery "Load More" settings - for speed up your site