My due date was changed today

I'm so confused lol.. I went to my appt today which I would have been 16 weeks this Friday. But at my appt today and due to an ultrasound last week due to some spotting they changed my due date from April 14 to March 28. When he measured my stomach externally he said I was 17 weeks and based off the ultrasound from last Wednesday the baby was measuring 16 weeks 5 days on that day.. They scheduled me for my next appt in 4 weeks Nov 23 where they will do the anatomy scan. I already know its a boy from the genetic screening I had at 10 weeks.. I'm just confused as hell now lol.