overwrite a woocomerce page

i have a theme with custom woocomerce page in my_theme/woocommerce/* , and have created a plugin to do some customization , so i created my_plugin/woocommerce/form-checkout.php to overwrite my_theme/woocommerce/checkout–/form-checkout.php
but the problem is that it can’t recognize wc functions (Call to undefined function wc_print_notices() .. etc )

this is my plugin code to overwrite it
the function :

public function customize_theme_pages( $page_template ){
        if ( is_page( 'shop-checkout' ) ) {
            $page_template = plugin_dir_url(__FILE__). 'woocommerce/form-checkout.php';
        }
        return $page_template;
    }

and the filter :
add_filter( 'page_template', array($this,'customize_theme_pages') );