Yep, you signed a valid contract, you are bound by the terms of the contract. If you are not underage to work, then you are bound by the contract and any and all laws under the Employment Act will pertain to both you AND the employer/agency.
Screw around with them and you will get a bad reputation that may follow you around for a long, long time.
SOME PEOPLE TRY TO TURN BACK THEIR ODOMETERS. NOT ME. I WANT PEOPLE TO KNOW WHY I LOOK THIS WAY. I'VE TRAVELED A LONG WAY, AND SOME OF THE ROADS WEREN'T PAVED. ~ Will Rogers