Sorry to hear you have PCOS but do not be concerned many women with PCOS do manage to get pregnant (Victoria Beckham is a well known case). I think it likely that you have had a period because one of your eggs ovulated properly and got through so causing you to have a period. This does not mean that your hormones are necessarily right again (although they could be) but it does give you a great chance of getting pregnant. I am not a doctor but know a little about PCOS, sometimes going on the oral contraceptive pill can help your system by damping it down, then when you come off it kick starts your system and may help you get pregnant. The ultrasound will show more information.
Good luck with your scan, make sure you ask the doctors what treatments you can have to help you get pregnant.