Okay I'm so confused

Abby • Mon, Jun 13

Originally in my due date was October 6 but at my 21 week weighed 1lb and they know the gender at 13 weeks before I got my blood test back..my conception date was the end of December my question is how am I dye in October because right now I'm six months if I go all the way to October there way longer than nine months they also moved my due date a day back