Absent a written contract or union protections--employees in 49 of 50 states are at-will employees. (Montana). As a waitress you were almost certainly an at-will employee. I am sure you have already researched that as an at-will employee, you can be fired for any or no reason (absent discriminatory dismissal).
Recommend you go back and discuss the matter with your manager--see if after a day or two, the reasons for your dismissal can be discussed.
On what you posted here, looks like the manager didn't appreciate you jumping the chain of command.
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You are an at-will employee absent an employment contract. But you should talk with a knowledgeable wage/hour lawyer to see if you were properly paid. Reminds me of a case I had a few years back.
I agree with the others. You were most likely you were an at will employee subject to being terminated for no reason at all.
This response is meant to be information only and should not be considered to be legal advice. This information is not meant and should not be construed to be the formation of an attorney client relationship. I practice Virginia Workers compensation law and Social Security Disability law.