I want to get a saturday job but I'm too shy so i think i'll mess up. What do I do? Advise?

uh...at some point, you will need a job.

At some point EVERYONE messes up.

When you are young, you'll find people have a lower expectation and a higher tolerance of screw ups as long as you are honest about them and learn from them

Job hunt.

Lol I'm shy too, but I'm doing the best to find a job
You'll have to get over being shy some way in order to get a job.

Smile and nod.

overcome your personal problems first. an employer does not need additional problems