Did I stole intentionally?

So 3 years ago I went to Goodwill to buy books about dinosaurs and dragons because they are cool. It was 7 books. I went up to the cashier to purchase the books. The cashier was someone I know who used to work at Wal-Mart. He scanned all the books that I wanted to purchase and what I noticed is that only 3 books were scanned and the other 4 weren't. I told him about the other books weren't scanned and then he told me that it's a discount, which I guess he means he's giving them to me for free. So I told him again about the other books not being scanned to the register and he told me to stop talking. So after that I paid for what was scanned and went on my day. I really didn't steal the books that weren't scanned? I wanted to go back and pay for the books, but I don't want to make the employee think he's letting me steal. I feel bad about it so I decide to make it up by making a cash donation of 5 dollars for the books that weren't scanned. Looking forward to hearing from you to see what you guys think about this.