If you need to cancel a card order (before the card is activated), you have two options.
If you have Account Owner or Admin rights, go to your Cards tab, select the card you've just ordered, click on "Mark as lost / unused / damaged / stolen". Then, click on Order a new card if you need to order another one.
If you don't have Account Owner or Admin rights, ask them to do it for you. It's indeed not possible for a Requester to cancel their card if it's not activated.
If you're unsure of who your Account Owner or Admin is, reach out to your favorite support team at email@example.com 😉 .