Yo extendíRegistrationFormUniqueEmail

class CustomRegistrationFormUniqueEmail(RegistrationFormUniqueEmail):
    first_name = forms.CharField(label=_('First name'), max_length=30,required=True)
    last_name = forms.CharField(label=_('Last name'), max_length=30, required=True)
    def save(self, profile_callback=None):
        new_user = super(CustomRegistrationFormUniqueEmail, self).save(profile_callback=profile_callback)
        new_user.first_name = self.cleaned_data['first_name']
        new_user.last_name = self.cleaned_data['last_name']
        return new_user

luego cambió de vista

#       form = form_class(data=request.POST, files=request.FILES)
        form = CustomRegistrationFormUniqueEmail(data=request.POST, files=request.FILES)

Pero, todavía veo el formulario predeterminado que contiene solo cuatro campos.