category_id=3 should just be cat=3
<?php query_posts('post_type=post&cat=3&post_status=publish&posts_per_page=10&paged='. get_query_var('paged')); ?>
<?php if(have_posts()) : ?>
<?php while (have_posts()) : the_post(); ?>
<h2><?php the_title(); ?></h2>
<p><?php the_content(); ?></p>
<?php endwhile; ?>
<?php endif; ?>