Set your featured products per row to the total number you want to use, then add to your stylesheet
Code:
#indexHomeBody #indexDefault {overflow: auto;}
#featuredProducts {width: 1920px !important;}
This will give the featured container the width it needs to hold all of the images (adjust to match your total images+margins width), and the overflow: auto; will make a horizontal scrollbar appear so the content width doesn't force the page to expand. The #indexHomeBody limits the scope to only the homepage.