Advice!

Victoria
So when I went for my first ultrasound the dr said by the baby's size I was 8 weeks and 5 days. So that's what I've been using for this app to know how far along I am. Well Tuesday I had a gender ultrasound. I was supposed to be 14wks3days but the baby measured 15wks1day. So now I don't know which one to go by.