Company fuel record doesnt match mileage record?

Got and email from boss to meet at his office once I return from vacation. He said that the fuel charges dont match the mileage record. I havent been puttin the right mileage each time I pump because I'm lazy. I told him that my actual mileage is different than those reports. I'm shaking because I dont wanna lose my job over being lazy. Will I lose my job or get written up (which I'm okay with)?