I wont advice you take Fort Pitt as 1st choice cos it is distance based. RGS is score based, we live in Essex. my DD score 625 and she got into Rochester automatically but Fort Pitt placed her on waiting list till date. Though we moved to Medway Few weeks now.
If Fort Pitt is your genuine first choice school, then you should put it as your highest preference on your CAF. It doesn't affect your chance of getting a place at any other school, you may find that in fact this year you are within the distance to which places are offered and even if not, your DD will be on the waiting list. Going on the waiting list for a school you ranked below the one you are offered is not automatic and in some areas you would have to go to appeal to be considered for a place. (I have no idea what the situation is re that in Kent / Medway).
Your LEA tells you to list schools on your CAF in your true order of preference for a reason...