family not allowing me to have early sexting scan

I am 20 years old and currently 16 weeks pregnant, my dad is currently very against me having an early sexting scan, he is very controlling and is demanding that I have to have one when I am 20 weeks as right now is too early and it will be wrong, I am completely heartbroken by this and feel there is nothing to do about it, I want to just see my baby again I don't want to have to wait another month! I feel he is telling me what to do and I have no choice in the matter, I don't even care if the gender they give me is wrong I just want to see my baby again to make sure they are happy and healthy, what should I do? :(