manual excerpt help

Hi there,
im developing a bespoke WordPress theme for the first time & im having difficulties getting the manual excerpt working correctly.

I have this in my functions.php:

//Get the excert function for limiting the length of the words of the front homepage news boxes
function get_excerpt($count){
$permalink = get_permalink($post->ID);
$excerpt = get_the_content();
$excerpt = strip_tags($excerpt);
$excerpt = substr($excerpt, 0, $count);
$excerpt = substr($excerpt, 0, strripos($excerpt, " "));
$excerpt = $excerpt.'<a href="'.$permalink.'">....</a>';
return $excerpt;
}

This is what i have on my blog page

<h2><a class="blogposttitle" href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h2>
                <span class="meta"><?php the_time('F jS, Y'); ?>   &nbsp;/&nbsp;    Posted by <?php the_author_link(); ?> &nbsp;/&nbsp; <span class="comments">&nbsp;<?php comments_popup_link(__('0 comments','example'),__('1 comment','example'),__('% comments','example')); ?></span></span>
<div class="dots"></div>
   <br><p><img src="<?php bloginfo('url'); ?>/imgresize.php?src=<?php echo $image_attributes[0]; ?>&h=200&w=800&q=100"></p> 

<?php echo  get_excerpt(800); ?>
 </div><!-- /#post-<?php get_the_ID(); ?> -->
        <?php endwhile; ?>

When i add a manual excerpt it just shows the standard text from the post & not what has been entered in the manual excerpt field. Is there anything i am missing?

Thank you