@ziawj2,
Han Meimei, that's also a bad excuse. Anyone with a half a brain will see right through it. Students miss appointments all the time, you really don't need an excuse, and you just have to own up to it.
But I don't know your cultural norms. Are excuse making a strict cultural norm in China?
If you must make an excuse, make it vague as possible with a hint of truth. Classic ones are transportation problems, feeling sick, you forgot, etc. Then again you can tell the truth.
Making excuses, in my opinion, is something that people do because they do not want to be responsible for their actions. I'd avoid it.