Commenting or remving get_sidebar(); won’t make it full with. Actually .content-area has 70% width defined in style.css.
Here are the possible solutions:
1. Add inline style to override the width
<div id="primary" class="content-area" style="width: 100%;">
2. Or add your own CSS class (e.g. full-width) on element and define in style.css
<div id="primary" class="content-area full-width">
.full-width { width: 100% }
Hope this will help.
