Personally, I'd call them.
A couple of days ago, I had a light meal and coffee at a cafe. A few of us were talking and I unintentionally walked out without paying. I realised this when I arrived home, rang the restaurant, and returned the next day to pay what was owed. They had no way of tracing me - but it was the right thing to do.
It is your decision, your kamma.
---The trouble is that you think you have time---
---Worry is the Interest, paid in advance, on a debt you may never owe---
---It's not what happens to you in life that is important ~ it's what you do with it ---