How can I fix/what should I change to fix the layout of my site?

When you use sites like Canva to publish a site, it is beautiful. So is Wix, but the white space margins on the side are driving me freaking CRAZY. In Canva, the layout is spread across full screen, and doesn’t have the confusing margins and columns. Am I sizing things wrong? What am I missing? This is one of the only things holding me back