Since you are not married, you cannot file as married, only single or head of household if you qualify as such. You need to change your filing status to single in the federal information section.
I think you may have misinterpreted my question.
My girlfriend and I are registered domestic partners in California. We file as single with the IRS. On the California return we want to file as RDP filing separately. When I do that, the software changes my filing status from RDP to married. Is that a problem or is it designed to do that?