You must take him to small claims court. If you are under 18, someone over 18 must file the lawsuit for you. How could you let it ride that much money owing? You should have quit sooner. You will win. Bring those checks and write down all the hours they owe you, and any witnesses to your babysitting, any emails or written documentation about your job.
Threaten to open a lawsuit if he doesn t pay and to give you a little bonus otherwise you d sue him for domestic violence.