Adding Custom Fields to Custom Post Type feed

gistfile1.aw

<?php

add_filter( 'the_content_rss', 'iculture_add_custom_fields_to_apptopvijf_content' );
add_filter( 'the_content', 'iculture_add_custom_fields_to_apptopvijf_content' );
/**
* Alter the content output for the apptovijf custom post type.
*
* @global $post Post object
* @param string $content Existing content.
* @return string Filtered content.
*
*/
function iculture_add_custom_fields_to_apptopvijf_content( $content ) {
	global $post, $id;
	
	// Skip filter if not CPT apptopvijf
	if ( 'apptopvijf' != get_post_type( $post->ID ) )
	     return $content;

	// do filtering
	$app_name  = get_post_meta( $post->ID, '_iculture_app_naam', $single = true );
	$dev_name  = get_post_meta( $post->ID, '_iculture_ontwikkelaar_naam', $single = true );
	$app_stars = get_post_meta( $post->ID, '_iculture_stars_app', $single = true );
	$price_app = get_post_meta( $post->ID, '_iculture_prijs_app', $single = true );
	$uni_app   = get_post_meta( $post->ID, '_iculture_uni_app', $single = true );
	$app_link  = get_post_meta( $post->ID, '_iculture_app_link', $single = true );
	$app_icon  = get_post_meta( $post->ID, '_iculture_app_icon', $single = true );
	
	
	
	$content = '<p class="app-naam">'. $app_name .'</p>
			    <p class="dev-naam">'. $dev_name .'</p>
			    <p class="dev-naam">'. $app_stars .'</p>
			    <p class="dev-naam">'. $price_app .'</p>
			    <p class="dev-naam">'. $uni_app .'</p>
			    <p class="dev-naam">'. $app_link .'</p>
			    <p class="dev-naam">'. $app_icon .'</p>' . $content;
	
	return $content;
}