Please help me

Jordyn

Okay so. I am currently 27 weeks 5 days. Due October 20th 2018. However...looking back at my ultrasound in the beginning the baby was measuring 7 weeks 2 days on Feb 28th...which means jan 10th he was conceived ? But my last period was Jan 8th-12th maybe usually 5-6 days long. 30 day cycle. Something isn't adding up?