“Can my boss report me to the IRS as a contractor if I don’t sign a form to say that I am his contractor?”
That depends – are you a contractor? If you are on the company payroll, then no, he probably can’t report you as a contractor – because he’ll be reporting you as an employee. If you are not on the payroll – and you are clearly working for him, as you yourself are calling him “your boss – he certainly can (and should) report what he is paying you. Being a contractor does not require you to sign a ‘contract’.