Job interview today!! - Help?

I have a job interview today and Im not sure what to expect.

Im 15 years old, applying for a job as a sales assistant at bakers delight (bakery). Its a junior position and part time.

What should I wear? What should I expect to be asked? I also have a problem. My Dads friend wrote my CV and it says certificates available on request - I dont have any!!!! Will she ask for them or not because its not a very important job!

Im worried. What will she ask me? Ive already talked to her about my hours if I get the job and then she told me to come today for an interview.

Please help me! What do you think
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This is not a high paid job so the interview is likely to be fairly casual. Make sure that your hair face and hands are all spotlessly clean and put on either no or very little makeup. Look her in the eye and try to relax she will know that you are nervous and will understand. Wear good casual clothes not jeans and not a T shirt. It is too late now but in future make sure that your CV is accurate just in case you are asked to produce the certificates , which anyway a person would normally bring to a job interview.