Return vs Echo Shortcode

Ok, so I’ve created a short code which echo’s some of the output; the problem I discovered is that the values must be returned instead of echo’d. I’m having problems converting the shortcode to return the date instead..

I’ve tried and it breaks my shortcode..

What would this shortcode code look like if it returned the code correctly instead of echo’ing it?

// [service slug="foobar"]
function services_shortcode( $atts ) {

    // Attributes
    extract( shortcode_atts(
        array(
            'slug' => '',
        ), $atts )
    );

if ( isset( $slug ) ) {
    $args = array( 'post_type' => 'cbd_services', 'name' => $slug ); // -1 Shows ALL Posts
    $loop = new WP_Query( $args );
    while ( $loop->have_posts() ) : $loop->the_post();
    $custom = get_post_custom($post->ID);
    $galleryPhotos = unserialize($custom["gallery_photos"][0]);
 ?>
    <div class="accordion closed">
        <h4 class="accordionTitle"><?php the_title(); ?><span>+</span></h4>
        <div class="accordionContent">
            <?php the_content(); ?>
            <?php if(!empty($galleryPhotos)){
                foreach($galleryPhotos as $photo){ ?>
                    <div class="photoContainer">
                        <a class="fresco" data-fresco-group="<?php echo $slug; ?>" href="https://wordpress.stackexchange.com/questions/139096/<?php echo $photo["gallery_imagesrc']; ?>">
                            <div class="hover">#makeitbigger</div><img src="<?php echo get_template_directory_uri(); ?>/thumb.php?src=<?php echo urlencode($photo['gallery_imagesrc']); ?>&w=452&h=275&zc=1" />
                            <span class="photoCaption"><?php echo $photo['gallery_title']; ?></span>
                        </a>
                    </div>
            <?php   }
            } ?>
        </div>
    </div>
<?php  endwhile; wp_reset_query();

}}
add_shortcode( 'service', 'services_shortcode' );

Just define a variable, and concat all html as string and return it.

<?php
function services_shortcode( $atts ) {

    // Attributes
    extract( shortcode_atts(
        array(
            'slug' => '',
        ), $atts )
    );
$html="";
if ( isset( $slug ) ) {
    $args = array( 'post_type' => 'cbd_services', 'name' => $slug ); // -1 Shows ALL Posts
    $loop = new WP_Query( $args );
    while ( $loop->have_posts() ) : $loop->the_post();
    $custom = get_post_custom($post->ID);
    $galleryPhotos = unserialize($custom["gallery_photos"][0]);

    $html.='<div class="accordion closed">
        <h4 class="accordionTitle">'.get_the_title($post->ID).'<span>+</span></h4>
        <div class="accordionContent">'.get_the_content();
        if(!empty($galleryPhotos)){
                foreach($galleryPhotos as $photo){ 
                    $html.='<div class="photoContainer">
                        <a class="fresco" data-fresco-group="'.$slug.'" href="'.$photo['gallery_imagesrc'].'">
                            <div class="hover">#makeitbigger</div><img src="'.get_template_directory_uri().'/thumb.php?src=".urlencode($photo["gallery_imagesrc']).'&w=452&h=275&zc=1" />
                            <span class="photoCaption">'.$photo['gallery_title'].'</span>
                        </a>
                    </div>';
              }
            } 
        $html.='</div>';
    $html.='</div>';
    endwhile; wp_reset_query();
    }

    return $html;
}
add_shortcode( 'service', 'services_shortcode' );