I'm afraid that now the transaction is pending we would be unable to cancel this for you. Please note that it usually takes up to 10 days for merchants to process a pending payment, however car rentals and hotel reservations can have a hold period of 30 days.
Whilst the payment is pending, interest will not accrue against that amount. Once the transaction clears you can always make a repayment to the account in the Repay section of the App by tapping "pay now".
If the order has already been cancelled with the merchant then the transaction will simply drop off and the amount will be added to your available balance once again.