Relieve

I  shopped at the Watson yesterday to buy some items neeeded in the house.After I went back, I realized that only three items were shown in my payment receipt, but I bought five items actually! It must be the cashier omit two things that I have been bought! So, I feel uncomfortable for the whole night. This morning I go to Watson again, and tell the cashier about his omission of counting the items.Then, he look at the receipt, feel like remember about something. The cashier say “Thank you” to me  immediately , because I pay back the money.  After I pay the money, he say “Sorry” to me, because of  inconvenienced me. I pay the money not because of his gratitude or apology, however, I am relieved after pay back the money.