Grid View Displays 4 columns instead of 3

Hi, please advise how to force the listings to display in 3 columns not 4

I have tried using the Page builder (code below) and Listing shortcode options but both just give me 4 columns by default.
Example here

[pt_core_listings element_name=”PN listings” type=”listing_type” style=”grid” nav=”1″ num=”50″ query=”taxonomy=listing&term=palmerston north” item_class=”col-md-3 col-sm-6 col-xs-12″ extra_class=””][/pt_core_listings]

and also

[LISTINGS cat=’9379′ orderby=title order=rand grid=true show=50]

Please advise how to make them display in 3 in all cases

Thanks