I wouldn't worry to much until you go see the specialist. Theres nothing you can do at this point to change it or fix it. Just continue eating healthy and continue doing what your doing. Dont over think this until you know more. Good luck to you.
The im expecting app isn't tailored to every individual pregnancy. It just gives you thedetails information that's happening in the week your in. So you can't rely on this app as a way to say my baby is doing fine it just gives the basic information about how the baby should be developing.
Maybe they got the dates wrong....stay positive..i'm sure they just want to be safe