Was I wrong?

So I went to khols today. I bought two pairs of jeans and a purse. We had a bunch of discounts (20% off sale, employee discount and khols card one ) so it was a total of 55% off. The cashier almost didn't scan the purse so I had to push it to her more and say you forgot this. When we left I was thinking there's no way that total was right ( around $13) so I looked at the receipt and she still after me telling her to scan the purse didn't scan it. So basically I got a free purse. My best friend was saying that is dishonest and it will come out of someone's pay check but how I see it is it was the cashier's fault not mine. Do you think I'm wrong?