Here if you scroll down to the contact section, you will see that the section is going full width, but it shouldn't because its parent container is set to remain boxed in.
Why is this happening?
From a quick look, the contact form fields are centered, with a left and right column. This is on a laptop display; didn't check other devices.
But, the best way to diagnose this is with the Developer Tools. Right-click your form area, select "Inspect Element" (or whatever or F12), then poke around looking at the CSS that is being used for the various elements.
Note that this place is not for CSS-type questions, it's for WordPress development; not plugins, not themes, not CSS, not JS, not PHP. It's best to post your question in the appropriate Stack Overflow area....you'll get faster/better answers there.