Cannot modify header information – headers already sent error

I get…..
Warning: Cannot modify header information – headers already sent by (output started at /home/nfleming/public_html/nicolefleming.com/blog/wp-content/themes/Minimal Horizontal.zip Folder/functions.php:2) in /home/nfleming/public_html/nicolefleming.com/blog/wp-includes/pluggable.php on line 868

I pretty sure it’s the php not liking where the html is in my functions.php which is below, i’m not that good with php how can i rework the code for it to work?

<?php

if ( function_exists('register_sidebar') )
    register_sidebar(array(
        'before_widget' => '<div class="block">',
        'after_widget' => '</div>',
        'before_title' => '<h5>',
        'after_title' => '</h5>',
    ));
?>

<?php
function completeTheme(){
echo '<div id="arrows">

<ul>
		<li class="lb"><a href="#container" title="Home">Home</a>
		<li id="left" class="lb"><a href="//" title="go left"><</a>
		<li id="right" class="lb"><a href="//" title="go right">></a>

<li><a href="#subcontent" title="Footer">Navigate</a></li>
</ul>
</div>
<div id="footer"><b>Designed by: </b><a href="http://www.gregponchak.com">Greg Ponchak</a> | <b>Sponsored by: </b><a href="http://www.gossipbingo.co.uk
">Free Bingo, <a href="http://www.moonbingo.com
">Bingo, <a href="http://www.lordbingo.co.uk/gala-bingo.html
">& Gala Bingo</div>
</div>
 </body>
 </html>';
}
?>