Display Thumbnail and Excerpt for first post, other post no display

<?php $first = true; ?>
<?php query_posts('category_name=uncategorized&posts_per_page=3&order=DES'); ?>
<ul>
<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>
<li>
    <?php if ( $first ): ?>
         <div class="img">
            <a href="<?php the_permalink(); ?>"><?php the_post_thumbnail('thumb-header'); ?></a>
        </div>
        <?php endif; ?>
<div class="title-widget">
    <a  href="<?php the_permalink(); ?>"><?php the_title(); ?></a>
</div>

    <?php if ( $first ): ?>
        <div class="des-widget">
            <?php custom_excerpt(10, ' ...') ?>
        </div>
          <?php $first = false; ?>
        <?php endif; ?>

</li>
<?php endwhile; ?>
<?php endif; ?>
</ul>