How to remove margin on a custom template

Hi there, I created a custom template just for the home page on the site, but there is a margin around the main content box.

I was just wondering how I could remove that so that if I inserted a image it would be exactly in the top left corner of that box with no padding or margins so I can position banners and content properly as the page is going to be mostly made up of full width banners…

Here is the code for the page template I made so far,

<?php
/*
Template Name: My Custom Template
*/

get_header(); ?>
    <div id="content" class="page col-full">
		<div id="maincustom" class="fullwidthcustom">
    <?php if (have_posts()) : while (have_posts()) : the_post();?>
    <div class="post">
        <div class="entrytext">
            <?php the_content('<p class="serif">Read the rest of this page »</p>'); ?>
        </div>
    </div>
    <?php endwhile; endif; ?>
<?php edit_post_link('Edit this entry.', '<p>', '</p>'); ?>
</div>

</div>
<?php get_footer(); ?>

and then I added this into the custom css

#maincustom .fullwidthcustom {
	width: 980px;
	padding: 0;
	margin: 0;
}

I hope this makes sense to someone as I really don’t know what I’m doing!

Thanks in advance, replied would be much appreciated!

http://casper-creations.com