How do I change the page layout to make all text span across the container?

You would have to use custom CSS to adjust that. Please try applying this code:

.page .post-title-wrapper {
    float: none;
    margin-bottom: 5%;
    width: 100%;
}
.page .post-content-wrapper {
    float: none;
    width: 100%;
}

You can enter the code by going to “Apperance > Customize > Additional CSS”.

If you would also like to use custom CSS for other elements, we would recommend Developer Tools on Chrome or Firebug on Firefox to inspect the elements on the page. Then you will know which CSS selector to adjust.

More info: https://uxbarn.com/inspecting-elements-developer-tools/