Qantas does allow fixing issues on same day - e.g. booked wrong day - but given that you chose to cancel, then you will get the refund as per the refund policy for the fare booked

You have no recourse - the benefit offered is beyond what it is required to offer

Given the policy requiring the passenger to be a FF member and that flight has to be > 30 days away, cannot see that you will have any success - the system will have automatically processed the correct refund amount