Hello,

You can set the full-width in the Theme Settings > General > Layout.

I am checking and I do not see any problems with the gap: https://gyazo.com/c38b19b2ed857e66c04f5a01df4740ba and https://gyazo.com/7c836c3b45ea9e58ffb1d884ccec0af6

Please try to disable this plugin: https://gyazo.com/9c50c3ff54f04b6c416ee94634c5fccc

Alternatively, add this code to the Theme Settings > Custom CSS > Global:

body .woocommerce-variation-add-to-cart {
    margin-top: 20px;
}

Best Regards