BuddyPress.org

I am using this code to display an excerpt from an extended profile field.

<?php	
      $profile_story = bp_profile_field_data( 'field=3&user_id=' . bp_get_member_user_id() );
          if(strlen($profile_story) > 50)
            $profile_story = substr($profile_story, 0, 50); 
?>
<p><?php echo $profile_story; ?></p>

I have it in the members-loop and I keep getting the full content, instead of just an excerpt. What am I doing wrong?