Will I be billed for Labels that I haven't used?

No.

BorderGuru only invoices shipments that have been processed at our hub. That means, if you cancelled an international order before you shipped it, you will never see this shipment show up on a BorderGuru invoice.

That being said: If you cancel a BorderGuru order on shopify, the BorderGuru label still remains active in our system. If such a label does show up on a shipment at our hub, we will process and bill it as normal. The status of the order in shopify as such has no influence on whether a BorderGuru shipping label is active or not.