Yes, you cancel a forward order at any time from creation to execution. This will cancel any outstanding pre-authorisation on your card and release the funds.
What is a pre-authorisation?
A pre-authorisation is a temporary hold of a specific amount of the available balance on a credit or debit card that is provided upon booking. The pre-authorisation is not a charge and no funds have been debited from your account. However, it could take 3-4 days for those funds to show back into your account. Please note that the pre-authorisations expire naturally within 7 days, so if you created the Forward Order more than 7 days ago the funds will already have been released.