Any tickets bought using a Railcard are not valid if you can't show a valid Railcard when asked onboard by a ticket inspector. You may be also charged a fine too. Your Railcard needs to be valid at the time of travel. So if you’ve added a Railcard to your booking in error, or you realise it will have expired by the time you travel, you could always buy or renew your Railcard in time for your departure date.
Alternatively, if you don’t want to buy a Railcard, you can request a refund for your ticket.