Hired same day as I applied?

So I applied to Hy-Vee today and I got hired the same day, I was talking to my friend about it, and she said the reason I got hired so fast is because it's a managing tactic to hire like 20 people and keep like only 5, I'm 16 and this is my first job, I really don't want this on my record. Should I be worried that I'm going to be fired?

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