I have an interview in three days to be a waitress?

Normally businesses will ask if you have any planned vacations (how many, how long will they last, etc) when they are interviewing a potential employee. If they don't ask, you should probably find a way to mention it. How annoying would it be for that company to hire you, just for them to find out that you're going to go on vacation in less than a month?

This doesn't mean you won't get the job. A lot of places will work around your schedule if this has already been planned. But if they want someone to start immediately, you may not necessarily get the job. I've always let employers know if I had any planned vacations because it is the polite thing to do.