The “collage” style is enforced on the homepage, it cannot be turned off in the theme settings. Turning that style off in theme settings only turns it off on collection pages.
In the snippet file featured-products.liquid, replace <div class="grid grid-collage"> with <div class="grid grid-uniform">. In the same file, replace {% include 'product-grid-collage' %} with {% include 'product-grid-item' %}.
Direct link to snippet file: https://www.shopify.com/admin/themes/current?key=snippets/featured-products.liquid