Bilingual Ballet on "After changing footerä: Problems with header and copyright area"

Hi, I wanted to customize the copyright text from "Proudly powered by WordPress" to my own text. (This is my site: http://www.bilingual-ballet.com/ I use the twenty thirteen theme.)So I created a footer.php file in my child theme and entered the following text:

<?php do_action( 'twentythirteen_credits' ); ?>
<?php echo 'Copyright © ' . date("Y") . ' ' . get_bloginfo('name'); ?>

The copyright text changed nicely, but it created the following problems:

1. My header image moved 1 cm down, so there is a 1cm white line on top of the page now, which should not be there.
2.The default brown footer box disappeared
3.Even when I enter the following code to my childs style.css, the copyright text does not move to the center:
.site-info {text-align:center;}

Can someone tell me what to do? Thanks a lot in advance.