The 18 hours is the maximum number of hours that a minor can work in Tennessee, not a minimum.
If you're unhappy with your job, you should look for a new one.
From Tennessee Department of Labor:
There are no limitations on the number of hours that 16 and 17-year-old minors work. They cannot be required to work during school hours; nor can they work past 10:00 p.m. on nights preceding school days (Sunday through Thursday nights), unless their parents or guardians sign a Parental Consent Form. The Parental Consent Form would allow them to work no later than 12:00 midnight three of those nights while school is in session.
This answer should not be taken as legal advice, and is for general information purposes only. Any information in this answer does not create an attorney/client relationship. You should contact a licensed Tennessee lawyer to discuss the specifics of your case.
No case here. Go job hunting. Good luck.
If you would like a consultation, call (865) 522-9000 to make an appointment. The information you obtain at this site is not, nor is it intended to be, legal advice. You should consult an attorney for advice regarding your individual situation. We invite you to contact us and welcome your calls. Contacting us does not create an attorney-client relationship. Please do not send any confidential information to us until such time as an attorney-client relationship has been established.