Most arbitration clauses are enforceable, whether or not there's "consideration," i.e., whether you get something in exchange for the agreement to sue arbitration.
Generally if you don't have a written employment contract, then your employment is "at will" and you don't have the right to continued employment or to keep the employment terms you currently have or formerly had. "At will" means you can be fired, demoted, have your hours changed or reduced, have your benefits changed or reduced or eliminated, etc. etc., as long as the treatment isn't discriminatory due to your age, sex, race, national origin, etc.
Here your boss gave you the choice of signing this agreement or losing some training and some hours. You chose not to sign, and it could be that your boss will soon find a reason to fire you (although if you're "at will," they don't need a reason) because you wanted to keep the right to sue them in court rather than arbitrate.
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