In some cases, an error may occur whilst payment is being processed.
If a confirmation email has not been received (be sure to check your junk mail) it is more than likely the order was not successful.
In some cases, a pending payment may show up on your transactions even though the order was unsuccessful. This amount should be returned/the transaction should disappear within 48hrs.
If 48hrs has passed and the pending transaction is still showing on your statement please contact your bank/paypal directly.