Won’t show certain catagories

Sure you got the right category ids or page ids.

Put this after your include sidebar to check if you’ve got the right page

echo "<pre>"; print_r($wp_query->query_vars); echo "</pre>";

Also install the Reveal Admin IDs to make sure you’ve bot the correct ids:
https://www.ads-software.com/extend/plugins/reveal-ids-for-wp-admin-25/

Still doesn’t like it,it comes out on the id 315 page as no posts in your criteria when there is, ive got the correct id’s as i used the plugin that you said.
this is my curent version of the code

<?php
/*
Template Name: news
*/
include"header2.php";
include"sidebar.php";

?>
<div id=pagetitle><img src=https://www.******/*****/arrowsmallpurple1.png /><strong><?php the_title();?></strong></div><br />

<div id=maincontent>
<?php
if (is_page('147') ) {
$cat = array(1,15,55,35,19,16,17,14,13,18,20);
} elseif ( is_page('315') ) {
$cat = array(17);
}

$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(); ?>
			<?php
			//necessary to show the tags
			global $wp_query;
			$wp_query->in_the_loop = true;
			?>
			<div <?php post_class() ?> id="post-<?php the_ID(); ?>">
<div id=news><h2><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></h2></a></div>
<?php the_excerpt(); ?>
 <h4><span id=news>Written by <?php the_author();?> at <?php the_time();?> <a class="title" href="<?php the_permalink() ?>" rel="bookmark">Read More.... &nbsp; &nbsp <?php comments_number(); ?></a> </span></h4>
<?php endwhile; else: ?>
<div id=footerbg">
			<div class="alignleft"><?php next_posts_link('« Older Entries') ?></div>
			<div class="alignright"><?php previous_posts_link('Newer Entries »') ?></div>
		</div>

<p>Sorry, no posts matched your criteria.</p>
<?php endif; ?>
</div>
</div></div>
<?php
include"footer.php";
?>

in addition if this helps this is what
echo "<pre>"; print_r($wp_query->query_vars); echo "</pre>";
shows

Array
(
    [pagename] => news
    [error] =>
    [m] => 0
    [p] => 0
    [post_parent] =>
    [subpost] =>
    [subpost_id] =>
    [attachment] =>
    [attachment_id] => 0
    [name] => news
    [hour] =>
    [static] =>
    [page_id] => 0
    [second] =>
    [minute] =>
    [day] => 0
    [monthnum] => 0
    [year] => 0
    [w] => 0
    [category_name] =>
    [tag] =>
    [cat] =>
    [tag_id] =>
    [author_name] =>
    [feed] =>
    [tb] =>
    [paged] =>
    [comments_popup] =>
    [meta_key] =>
    [meta_value] =>
    [preview] =>
    [category__in] => Array
        (
        )

    [category__not_in] => Array
        (
        )

    [category__and] => Array
        (
        )

    [post__in] => Array
        (
        )

    [post__not_in] => Array
        (
        )

    [tag__in] => Array
        (
        )

    [tag__not_in] => Array
        (
        )

    [tag__and] => Array
        (
        )

    [tag_slug__in] => Array
        (
        )

    [tag_slug__and] => Array
        (
        )

    [caller_get_posts] =>
    [suppress_filters] =>
    [post_type] => post
    [posts_per_page] => 6
    [nopaging] =>
    [comments_per_page] => 50
    [order] => DESC
    [orderby] => wp_posts.post_date DESC
)