Adding a customm special field

Hi

I am adding a custom special field to the checkout using the code from http://docs.woothemes.com/document/tutorial-customising-checkout-fields-using-actions-and-filters/#section-4.

How do I make this print on print-delivery-note.php?

Here’s what I have done

on woocommerce-delivery-notes.php added after the wcdn_get_shipping_notes function

/**
 * Return has custom message
 */
if ( !function_exists( 'wcdn_get_message' ) ) {
	function wcdn_get_message() {
		global $wcdn;
		return wpautop( wptexturize( $wcdn->print->get_order()->my_field_name ) );
	}
}

/**
 * Show custom message
 */
if ( !function_exists( 'wcdn_message' ) ) {
	function wcdn_message() {
		global $wcdn;
		echo wcdn_get_message();
	}
}

which is a copy of the shipping notes function with a few changes. I then on print-delivery-note.php have

<?php wcdn_message(); ?>

I feel like I am close, I just can’t manage to grab my_field_name and print it to the delivery note.

Can you help?

https://wordpress.org/plugins/woocommerce-delivery-notes/