If I were you I wouldn't have worried

A similar thing happened to my mum a few weeks ago, we were in Kmart and mum chose a book and put it on top of the pram, we then walked around the rest of Kmart and got a few other items paid for them and went to the food court for lunch, mum was sitting there looking at DSs pram wondering what the square shape in the top was when she realised she had walked out without paying for the book, in this case I told her to go back and pay for the book, simply because she had legitimately forgotten it and we were still in the shopping centre