应该这样解释：I have some important things to do tomorrow, I'm afraid I couldn't meet you, maybe when I have time I could go, I'm very sorry! I hope you can understand me.
打电话给他,另找个时间在见面。 I'm sorry to tell you that I can not meet you tommorrow because of something urgent.I'm very sorry,and I want to know it is possible for us to meet at(时间）。
和老外不用解释太多,你只要告诉他你明天有事就行了. Sir or Madam,(名称), sorry that I have some unexpected thing to do tomorrow, shall we change our appointment to another day(or time) if it is suitable for you? Much appreciation for your kindly comprehension.
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