get_theme_mod not working

Hi
I have this in index

<?php
    $lay = get_theme_mod('layouts_sitting');
    get_template_part( 'loop', $lay );
?>

also I have this in customizer.php

function themez_customize_register( $wp_customize ) {
	    $wp_customize->add_section( 'themez_scheme', array(
	            'title'          => __( 'scheme' ),
	            'description'    => 'pick'
	    ));
		$wp_customize->add_setting('layouts_sitting', array(
		 	   'capability'      => 'edit_theme_options',
		 	   'default'         => 'index',
		));
		$wp_customize->add_control( 'themez_scheme', array(
			   'label'      => __( 'LAYOUTS', 'themez' ),
			   'section'    => 'themez_scheme',
			   'settings'   => 'layouts_sitting',
			   'type'       => 'radio',
			   'choices'    => array(
				    'index' => 'Choice 1',
              			    'index2' => 'Choice 2'
		));
}

add_action( 'customize_register', 'themez_customize_register' );

the idea is changing the loop from customizer panel
get_template_part( 'loop', $lay );
where $lay is index or index2
but it doesnt work so far
any help ??