Ascending Code Not Working in My Template

I have created a template page that lists all post titles in a specific category.

My page code works great but I couldn’t reorder it in date-ascending order.

I changed this:

<?php if (have_posts()) : ?>

to

<?php
query_posts($query_string . '&order=ASC');
if (have_posts()) : ?>

But it didnt work.

My template code is here:

<div id="content" class="section">

<?php
// page id 714 will get category ID 11 posts, page 718 will get category 3 posts
if (is_page('714') ) {
$cat = array(11);
} elseif ( is_page('718') ) {
$cat = array(3);
} elseif ( is_page('28') ) {
$cat = array(17);
} else {
$cat = '';
}

$showposts = -1; // -1 shows all posts
$do_not_show_stickies = 1; // 0 to show stickies
$args=array(
   'category__in' => $cat,
   'showposts' => $showposts,
   'caller_get_posts' => $do_not_show_stickies
   );
$my_query = new WP_Query($args);
?>

	<?php if( $my_query->have_posts() ) : ?>
		<?php while ($my_query->have_posts()) : $my_query->the_post(); ?>
			<div <?php post_class() ?> id="post-<?php the_ID(); ?>">
				<h4><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></h4>

</div>