[@robin-w Moderator 12 years, 7 months ago]

The page you are using to display is a full width page.

Since you are using a child theme of twenty twelve, I presume you still have the default template which has a sidebar.

If so, then copy this file, and rename it to bbpress.php and put it into your theme’s root ie
wp-content/themes/twentytwelve-Child/bbpress.php

That will ensure that bbPress uses a template with a sidebar