The Divi Theme supports several different types of "section" elements in its page builder. Two of these are the standard section and the fullwidth section. As the name suggests, a fullwidth section typically occupies the fullwidth of the browser window. A standard section, on the other hand has a fixed or limited width and usually sits centered in the page.
In some situations you might want to make a full-width section behave more like a standard section. For example, some modules only work in fullwidth sections (an example is Optimus Divi's breadcrumbs module). This means that by default their content extends to the edge of the page. Here's what you can do in such cases:
Restrict the content width of the fullwidth section
You can restrict the content width of a fullwidth section by going into the section's settings and setting the "Design > Sizing > Content Width" option to your desired width, as a percentage (80%, say). This will restrict the content width, but the content will remain on the far left of the page. To center the section, you go into "Design > Spacing > Custom Margin" and set the "Left" and "Right" margin to each be half of the remaining width (so in this example, that would be half of 20%, so 10% each).
You'll now have a fullwidth section with its content constrained to the middle 80% of the page, which should hopefully make it better fit the flow of the rest of your page content.