data is of type uint8_t so when you print out one of those elements, you are getting the ascii code associated with "xx1" in hex, it would be 78 78 31 but since you are printing it out as a decimal, you are getting 120 120 49.
if you create a string
char buffer[5];
.... // read the card
buffer[0] = data[9];
buffer[1] = data[10];
buffer[2] = data[11];
buffer[3] = '\0'; // terminate string
Serial.println( buffer );