In order to use the Full Width row type with WPBakery Page Builder, you should make sure that you’ve set Page Attributes > Template to Full Width as well:
If this is not the case, you’re most likely using the Default page template which means that page content is displayed in a grid. The default grid width is 1100px, unless you change this in Theme_name Options > General > Design Style > Initial Width of Content:
So if the Full Width template is not set for your page, your Full Width Rows will be as wide as your grid is (1100-1400px).