I’m glad you’re liking Sela!
Could you provide a link to a page or post where you’re seeing this empty space so I can take a look directly?
Sela comes with a full-width template for pages, but page templates aren’t applicable to posts or the blog index.
Once I see exactly where you want to remove the space where your sidebar was, I’ll be better able to help.
I also noticed your site is hosted over on WordPress.com. If you have more questions in the future, please post over in the WordPress.com forums:
http://en.forums.wordpress.com/
Tips on getting help in the WordPress.com forums:
http://en.support.wordpress.com/getting-help-in-the-forums/
I also noticed you haven’t yet assigned your blog posts to be displayed anywhere. If you’d still like folks to be able to read your posts, you’ll need to do that by creating a dummy page, call it something like Blog or News, and assign it to display your latest posts as “Posts Page” under Settings > Reading.
