FB Thumbnail

Hi

I'm currently using the Theme "GameCenter" and wanted to add custom Facebook Thumbnails.
I put

<?php $yag_images = wp_get_attachment_image_src(get_post_thumbnail_id($post->ID), 'thumbnail' ); ?>
<?php if($yag_images != ''):?>
 <meta property="og:image" content="<?php echo $yag_images[0]; ?>" />
<?php else: ?>
 <meta property="og:image" content="IMG LINK" />
<?php endif;?>

into Theme Settings -> integreation -> head code
but it didn't work. I wanted to ask if there is another solution or where to put it instead.

Thanks