It doesn't matter what your reason is. You're a grown-up, so if you want to cancel a date, then cancel it. To be honest, I was flabbergasted by the subject of your thread - do you really need people you don't know to tell you it's okay to cancel a date you don't want to go on? Don't go if you don't want to!
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein