Don't worry, you haven't really been charged twice!
If you still see a pending transaction on your bank statement after you have already paid for a successfully completed order, know that this is not a charge, but an authorization hold that has yet to be released by your bank.
After you enter your card details or swipe your card, many merchants are then required to send a pre-authorization check to your card issuer to ensure that there are enough funds in your account and to "save" that amount for when the transaction is completed.
If you cannot wait that long, then reaching out to your bank should do the trick. Some banks request the order's authorization hold or written confirmation from the merchant in order to release the hold. If your bank requested this from you, then please let our Happiness Heroes know.