Small head

At 20weeks i went for my anatomy scan and my babys head was measuring small but brain and everything looked great. My doctor said if it made me feel more comfortable i can get another scan. I said ok I’ll wait until I’m further along. I went yesterday at 29 weeks. I won’t know anything until i see my actual doctor next week but they told me to come back in 4 weeks for another scan. This concerns me because i feel like If my baby was measuring fine

Then i wouldn’t need to come back. I’m just trying not to freak out because everything else about her is fine.