Sorry to hear that there are some problems getting your post content to display in full-width Andrea, our team will do everything we can to help!
The width of your Post and Page content can be changed using the Section Width toggle in the Post and Page Builder Visual editing tools.
You can change the width of a particular block on your page by click the Edit Section button that appears in the gray Section tools that shows up when hovering over a Section in your Post or Page content. The Section Width option toggles the width of that element between Full-Width and Contained settings.
Please let us know if you have any other questions for us!