help with 2012

I set up a 2012 child theme. On my homepage, I just want excerpts and an image as a read more link. I changed <?php the_content( __( 'Continue reading <span class="meta-nav">&rarr;</span>', 'twentytwelve' ) ); ?> to <?php the_excerpt( __( 'Continue reading <span class="meta-nav">&rarr;</span>', 'twentytwelve' ) ); ?> but when you click on the post title it still only shows the excerpt and not the complete posts. How can I fix?