Image Choices works with Gravity Forms CSS Ready classes (https://www.gravityforms.com/css-ready-classes/) specifically the List classes. So for example the
gf_list_5col class will give you rows of five choices, etc. Just add the relevant class to the CSS Class in the field’s Appearance tab.
Newer versions of Image Choices now comes bundled with themes which allows for setting the column numbers within the add-on settings.