custom post url rewrites

Made a custom post type in functions.php

add_action('init', 'fossil_post_type_register');

function fossil_post_type_register() {

	$labels = array(
		'name' => _x('Fossils', 'post type general name'),
		'singular_name' => _x('Fossil', 'post type singular name'),
		'add_new' => _x('Add New', 'portfolio item'),
		'add_new_item' => __('Add New Fossil'),
		'edit_item' => __('Edit Fossil'),
		'new_item' => __('New Fossil'),
		'view_item' => __('View Fossil'),
		'search_items' => __('Search Fossils'),
		'not_found' =>  __('Nothing found'),
		'not_found_in_trash' => __('Nothing found in Trash'),
		'parent_item_colon' => ''
	);

	$args = array(
		'labels' => $labels,
		'public' => true,
		'publicly_queryable' => true,
		'show_ui' => true,
        'show_in_menu' => true,
		'query_var' => true,
		'menu_icon' => 'dashicons-plus-alt',
		'rewrite' => array('slug' => 'fossil', 'with_front' => FALSE),
		'capability_type' => 'post',
		'hierarchical' => false,
		'menu_position' => null,
		'has_archive' => true,
		'supports' => array('thumbnail', 'comments')
	); 

	register_post_type( 'fossil' , $args );
}

All I want is for the url mysite.com/fossil/%post_id/ to load the use the page single-fossil.php to display the information on that custom post and for the url mysite.com/fossil/ to use the page archive-fossil.php to show all of posts of this custom type.

Currently my permalink is using custom structure /%post_id%/. No matter how I fiddle with the rewrite slug or change permalink structure I can’t get the urls to display the content I want. I’m sure I could you wordpress rewrite and define my own custom rewrites but I feel like that is overkill for what I’m trying to accomplish? Anyone have a clue where I am botching this?