I'm sure as long as you don't start to efface and dilate you're fine. I don't know about the cervical length either, but I never had it mentioned to me at all when I was pregnant, until I was 33 weeks and started to efface.
Well, actually your doctor would make more money for treatments and things so I don't see why he'd just turn you away if you had a serious issue. I have no idea what the cervical length is supposed to be. I was just told mine was "long and closed".