Hi!
A. You have a custom CSS that forces 20% width on the search box parent widget element: https://i.imgur.com/KDgtKlb.png
I suggest either removing that, or using a custom CSS to change the min-width attribute of the search:
[html]#ajaxsearchprowidget-5 {
min-width: 100% !important;
}[/html]
Please note, that this is not directly related to the plugin, it is only a suggestion.
B. The column calculation depends on the seach final width, and on the initial width, that is defined on the back-end here: https://i.imgur.com/GFS80Dg.png
Lower value = more columns, higher value = less columns.
Once you fixed the width of the search bar, it will automatically adjust to the screen size, based on the defined results width.