My son has my last name, not his fathers. I was never married to his father and his father was no where around during pregnancy. His father now wants him to have his last name after a year. I live in CA... do I have to give my son his fathers last name since we were not married??

Unless it is ordered differently by a court, you absolutely do not have to agree to change the child's name.

In most cases, BOTH parents must agree to a name change for a child.