Genesis Simple new theme has a fullwidth of only 65%, and didn't go for fullwidth (100%), see example here https://demo.studiopress.com/genesis-sample/layouts/full-width-content/

So, if you need fullwidth for your homepage (or other pages) you can do 2 things; 1. Add css line at style.css & 2. Create custom page and add few line of CSS in your style.css file.

Option 1

Open your style.css, and add width:100% as show below

.full-width-content .content,
.landing-page .content {
    float: none;
    margin-left: auto;
    margin-right: auto;
    width:100%;
    max-width:900px;      
}

Option 2

1. Create new PHP page called 'page_home.php' inside your childtheme folder, and paste below code.

<?php
/**
 * Genesis Framework.
 *
 * Template Name: Homepage
  
 * WARNING: This file is part of the core Genesis Framework. DO NOT edit this file under any circumstances.
 * Please do all modifications in the form of a child theme.
 *
 * @package Genesis\Templates
 * @author  StudioPress
 * @license GPL-2.0+
 * @link    http://my.studiopress.com/themes/genesis/
 */
  
 //* Add landing page body class to the head
add_filter( 'body_class', 'genesis_sample_add_body_class' );
function genesis_sample_add_body_class( $classes ) {
 
    $classes[] = 'homepage-page';
 
    return $classes;
 
}
 
// Remove Post Title
remove_action('genesis_entry_header', 'genesis_do_post_title');
 
 
// This file handles pages, but only exists for the sake of child theme forward compatibility.
genesis();

2. Paste below css in your style.css file

homepage-page .content {
    width:100%;
    max-width: 1000px;
}
.homepage-page .site-inner {
    padding: 0 30px;
}

3. When you create new page select 'Homepage' at Template