Help with adding a logo to twenty ten child theme

Hello, I’ve create a child theme for a twenty ten and tried to add a logo but didn’t work, I don’t know what I missed

Firstly my url is: sitestobuyonline.com

What I did was created the style.css file to link the css from the parent and copy the heather.php file into the child theme and in this one I replaced this code:

<<?php echo $heading_tag; ?> id="site-title">
<span>
<a href="<?php echo home_url( '/' ); ?>" title="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" rel="home"><?php bloginfo( 'name' ); ?></a>
</span>
</<?php echo $heading_tag; ?>>

For this one:

<h1 id="site-title">
<span>
<a href="<?php bloginfo ('home');?>" rel="home" title="<?php bloginfo('name');?>">
<img src="<?php echo bloginfo ('stylesheet_directory');?>/images/logo.png" alt="<?php bloginfo ('name');?>" />
</a>
</span>
</h1><!--end of h1 site-title-->

Any idea?