When reading the card, depending on the amount of time to hold the card near the RFID antenna, read the information on the card several times.
Why do you think you'd get different answers?
My question is, how do I read only once the information, no matter how long the card is near the RFID antenna?
Most RFID readers do that for you.
You posted no code, although the rules for posting in this section REQUIRE you to. You posted no link to the hardware you are using. One can be forgiven for thinking that you don't really want help.