I think its slightly unfair of them to judge your entire ability to talk to customers on one test and one opinion. You should tell them that you can do the job of the busser, bussers really don't talk to people, that's more the waitress's job so I don't know what they're talking about. Next time someone questions your ability to handle anything, tell them you can handle it just fine and would work on improving. Sometimes you need to exude false confidence even if others are pointing out your mistakes, that's the only way people will give you another chance to prove yourself. Everyone has off days. If they cannot reschedule you, then tell them you want to keep your current job and that test did not show all of your qualities and skills and you feel you can handle customers just fine. Fake it til you make it. Don't let other people's opinions make decisions for your life. Don't agree to other people's opinions if it has a direct affect on your life. Stand up for yourself and don't be afraid, otherwise they will walk all over you.