Its a normal thing for an instructor to say. He wouldn't/shouldn't have allowed you to book your test if you weren't ready for it but it also looks bad on them if a student fails if they're not ready to test. Just do your lesson as normal, it's only to see if you make silly mistakes that would be unforgivable on a test, but if you're doing well then I wouldn't stress about it. not the end of the world really is it