Conditional Tag code not working

I’m trying to get a client’s “Blog” page to display a different right sidebar than the rest of the pages. I entered this into the page.php file of the template:

Where it used to say:

<?php include ('sidebar2.php'); ?>

I changed it to:

<?php
  if (is_page("blog")) {
  echo '<?php include ('sidebar2.php'); ?>';
  } else {
   echo '<?php include ('sidebar3.php'); ?>';
  }
?>

This code was taken directly from a site that it works on. All I changed is what is in the echo '' part and removed some elseif lines.

Can anyone tell me why this isn’t working? I think it’s because I have <?php ?> in there more than once but don’t know how else to write it.

Thanks