You cannot cancel a pending transaction because it has been already submitted for processing. Please wait until it is complete in your GunBroker Pay wallet. This can take 1-3 banking days.
After you see it complete in your GunBroker Pay dashboard, you can do another transfer as needed.
You can see the status of your GunBroker Pay account and transactions in your GunBroker Pay dashboard:
https://app.gunbrokerpay.com/login