going out of my mind can dates be wrong

Kristyanne
Ok so I'm due 9th of March making me 16weeks 
With my last child he was born early only meant to be two weeks early 
but after he was born they questioned it thinking he was early due to his development now I'm pregnant with twin I'm scared the same thing will happen as twins are often early it scares me more 
Has anyone ever given wrong dates by more then two weeks