Hi there,
Thanks for reaching out. Our free trial, as it name implies, is totally free. You didn't enter any credit card information to enroll to the free trial. Thus, there's no need to cancel, you can just stop using Labelmaker or uninstall it from the Google Workspace Marketplace.
In order for us to improve the product, can I ask you why you chose to not pursue with your trial ?
All the best,
Lucy