Wrap every 2 posts on a row

I'm using Bootstrap, I have a list of posts and I want to wrap every 2 posts on a row. Each post is wrapped on a <div col>. You can see live here.

I tried with this but it wrap the row each one post:

<?php 
$num = 0;
// Check if there are any posts to display
if ( have_posts() ) : ?>
<?php
// The Loop
while ( have_posts() ) : the_post();
if($num%2) { 
echo "<div class='row' style='margin-bottom: 2.3em;''>";
}
?>
<div class="col-xs-12 col-sm-6 col-md-6">
  <h2 class="category-encabezado">
    <a href="<?php the_permalink() ?>" rel="bookmark" title="Enlace a <?php the_title_attribute(); ?>">
      <?php the_title(); ?>
    </a>
  </h2>
  <small>Hace 
    <?php echo human_time_diff( get_the_time('U'), current_time('timestamp') ) . ''; ?>
  </small>
  <div class="entry">
    <p>
      <?php the_excerpt(); ?>
    </p>
    <?php
$my_shortcode = get_field('audio-field');
echo do_shortcode( $my_shortcode );
?>
  </div>
</div>
<?php
if($num %2) {
echo '</div>';
}
$num++
?>
<?php endwhile; // End Loop
?>
</div>
<?php