You can only use the gravity form add-on for Fancy Product Designer in non-WooCommerce products.
Open the field options and click on the "Appearance" tab and enter "fpd-order" in the Custom CSS class input.
Last but not least go to the Advanced tab and enable "Hidden" show this field is not showing up in the form.
Connect Fancy Product Designer with a GF form
Last but not least you have to use another shortcode to display the product designer in any post or page (no WooCommerce products) and to connect the product designer to a form.
Put this shortcode anywhere in the page. The page needs to include also the GF form that you set up for the product designer.