Help with adding fields to checkout

Hey,

i want to add some fields to my checkout and then have them visible in my orders but something goes wrong and i don’t know what exactly.

I have added 2 extra fields with this code:

// Hook in
add_filter( 'woocommerce_checkout_fields' , 'dropdown' );

// Our hooked in function - $fields is passed via the filter!
function dropdown( $fields ) {
     $fields['billing']['wenskaartje'] = array(
        'label'     => __('Wenst u een wenskaartje bij uw bestelling ?', 'woocommerce'),
    'placeholder'   => _x('dropdown', 'placeholder', 'woocommerce'),
    'required'  => false,
    'class'     => array('form-row-wide'),
    'clear'     => true,
    'type'      => 'select',
     'options'     => array(
        'option 1' => __('Ik wens geen wenskaartje bij mijn bestelling', 'woocommerce' ),
        'option 2' => __('Wenskaartje: Fijne verjaardag', 'woocommerce' ),
        'option 3' => __('Wenskaartje: Gefeliciteerd', 'woocommerce' ),
        'option 4' => __('Wenskaartje: Veel liefs', 'woocommerce' ),
        'option 5' => __('Wenskaartje: Van harte beterschap', 'woocommerce' ),
        'option 6' => __('Andere', 'woocommerce' )
        )//end of options
     );

     return $fields;
}

// Hook in
add_filter( 'woocommerce_checkout_fields' , 'custom_override_checkout_fields' );

// Our hooked in function - $fields is passed via the filter!
function custom_override_checkout_fields( $fields ) {
     $fields['billing']['tekstkaartje'] = array(
        'label'     => __('Tekst op het wenskaartje', 'woocommerce'),
    'placeholder'   => _x('Uw text voor het kaartje', 'placeholder', 'woocommerce'),
    'required'  => false,
    'class'     => array('form-row-wide'),
    'type'		=> 'textarea',
    'clear'     => true
     );

     return $fields;
}

i guess my variables are wenskaartje and textkaartje. Now i try to display them in my admin but the fields stay empty. Any idea why ?

add_action( 'woocommerce_admin_order_data_after_billing_address', 'my_custom_checkout_field_display_admin_order_meta', 10, 1 );

function my_custom_checkout_field_display_admin_order_meta($order){
    echo '<p><strong>'.__('Wenskaartje').':</strong> ' . get_post_meta( $order->id, 'wenskaartje', true ) . '</p>';
    echo '<p><strong>'.__('Text op het kaartje').':</strong> ' . get_post_meta( $order->id, 'textkaartje', true ) . '</p>';
}

Is it maybe because i still use wordpress 3.4.2 with woocommerce 1.6.5.2 ?

https://www.ads-software.com/plugins/woocommerce/