Check the bill
核对账单

May I have my bill, please?
我能结账吗？
That's $20 in all.
总共20美元。
Well, I am afraid you have made a mistake. Would you check it again, please?
恐怕你搞错了，能核查一下账单吗？

Let me see. I am terribly sorry, sir. That should be $18.
我看看。非常抱歉，先生，应该是18美元。
It doesn't matter.
没关系。