Display Data’s metabox in page

So far, all you posted is backend functionality.

Ob the frontend you have to actively display the data, as you already did in the backend.

Like so:

// assuming you're in the Loop on your INDIVIDUAL page template
echo wp_kses_post(get_post_meta(get_the_ID(), '_shortcode', true));

If you don’t have an individual template file, you have to check for the page ID, for instance like so.

// assuming you're in the Loop on your GENERAL page template
if (is_page(YOUR-PAGE-ID))
    echo wp_kses_post(get_post_meta(get_the_ID(), '_shortcode', true));