Sidebars are confusing in Twenty Eleven! Under the Appearance > Theme Options menu, The “One column, no sidebar” layout makes a narrow, single-column layout sorta like Tumblr. If you select either of the column layouts, and your homepage tis the default Recent Posts, you’ll get a two-column layout on the homepage and a one-column layout on individual Posts and Pages. But if you want a single-column homepage you’ll need to make a static page and set it as your homepage (Settings > Reading) and it will be single column. Then, if you want other pages to have sidebars, select Page Attributes > Sidebar Template from the editing window. You’ll need to select the Sidebar Template for every page that you want to have a sidebar. Hope this helps!