Right sidebar appears below content on post

Well, I´m not able to use right sidebar at post page, and I don´t know exactly why…

*So I don´t know if this is a question or a bug report, but here is what I´ve done:

As use default single post format did not work, I copied single.php to child theme and placed <?php get_sidebar(); ?> above this line: <section id="primary" class="site-content span8">

So I commented <?php get_sidebar(); ?> below this line: </section><!-- #primary -->

Then I used floated css to locate it at right side:
#st-content-wrapper #secondary { float: right; }

(at first, it was located at left side, when I changed get_sidebar(); code.

I don´t know if I made some mistake in order to not being able to use right sidebar at post. I´m using child theme.

But I´ve noteced that <div id="secondary" class="widget-area span4" role="complementary"> (at single.php) was not located at right side because div #primary was evolved with a .row class.