If you check the source HTML code of your home page, you can find the following CSS style applied:

@media (min-width: 992px) {
  .no-sidebars ul.subcategory-view-icons.subcategory-list.grid-list > li {
    float: left;
    width: 16.66666667%;
  }
}

So, by default, X-Cart shows 6 categories in a single row on the homepage.

If you need to show 3 categories in a single row on your homepage, you can implement the following Custom CSS in your X-Cart store back end:

@media (min-width: 992px) {
  .no-sidebars ul.subcategory-view-icons.subcategory-list.grid-list > li {
    float: left;
    width: 33.33333333%;
  }
}