unfair work treatment

i'm from ohio
i work as a customer service reprensitive and at work we have this option that we call "cut", which is if we don't get alot of calls then they will let up go home early.
as soon as i got to work i told my supervisor i needed to be cut because i had exams to study for the following day. she told me no, however, she let two employees go nearly two hours before there shift ended. when i approached her with this she smilled and told me "they found somebody to cover their shift", this was a bold face lie.
later on the same night she cut another employee who had the exact (exact) same hours as i. once again when i confronted her she said he got off at eight when i asked him (and looked at the schedule) "they" both said nine p.m., but my supervisor hinted (body signals) until he agreed and said eight.
now i wouldn't be so upset if this was the first time, but its not this is about the fifth time this has happened to me.
my mother, however, does know an employee at my work who she told to tell my supervisor to give me more hours(without my permission or approval) .
since im only sixteen, can my mother really do that, especially if i don't want more hours? or my supervisor when i have an english,cisco,and chemistry exam the following day? what should/can i do?
thank you

Unless you are part of a union or are under an employment contract that says otherwise, the employer is not under any obligation to give you more or cut your hours regardless of what either you or your mother requests. The fact that you have exams the next day is not binding of the employer - that's not their problem.

Unfortunately, in your situation, it's not illegal for your employer to be a jerk.

As cbg said, unless otherwise stated in an employee handbook or in a union or contract-type situation, you're pretty much stuck with what appears to be an unfairness in scheduling.