Debit card not charged?

Today (12/4) I went to a local coffee shop and ordered something to go. I accidentally slid my card prematurely, the cashier said slide again. And my purchase went through. But I wasn’t asked for my PIN number and I wasn’t handed my receipt. But when I checked my bank account a while ago the charge didn’t show up?? Did I do something wrong? This has never happened to me before. A friend told me that sometimes this thing happens and I’ll be charged later.