As for your concrete question:
You could theoretically parse the retrieved content before shortcodes are resolved for this specific one, set a flag and wrap the title on condition of that.
But it would make much more sense to trash the shortcode-approach and simply create a new page template.
(Especially so, given that the parsing for the shortcode, or at least its consequences, would have to happen in the used template file anyway)
Copy the contents of your theme’s page.php to a new file.
Call that page-narrow.php.
Prepend it by
<?php
/*
* Template Name: Narrow Page
*/
?>
And wrap the copied part in an element with the desired class.