Question slightly concerned

Had a growth scan last week and they wanted to check his heart again to make sure it’s good.

So today i went and his heart looks good. They want me to come back in three weeks tho because they said his head is measuring small? I don’t recall them saying this at the last ultrasound maybe because the heart talk concerned me more. So they said they aren’t worried about it and just wanna look. Should i be worried or should i take my dr word? They said his brain is developing fine they just wanna check. He’s head down and buried in my placenta.

Sorry i know i was wrong to google it but i did and scared myself. I do go see my midwife tomorrow and will ask.