do not hide the article

I do not want to display the article of the catid 3 in Home, so i use the code as below in the index.php of my theme:
<?php if (have_posts()) : query_posts($query_string .’&cat=-3′); ?>

BUT, now, i add a new page named “my blog”, and choose the template of “blog”, in the blog template, i copy the code all of the index.php, and when i visit the “my blog”, the article of the catid 3 will display, CAN NOT Hide.

Please help me! Thanks!