Thorntons

Hello, name is Raymond H. McCormick. I paid prepay inside the Thornton's gas station #630 for gas for my car Grey Malibu 2006 at pump #15 in the amount of $15 along with a couple of other things. My bill came to $17.10 altogether on my receipts. When I went to tell them my tank is full at $13.83, they said the rest will go back on the card I use to pay for the gas. So, $1.17 is going go back on my card I used to pay for the gas right? If I don't how do I get my $1.17 refunded to me?