Growing 6 days behind??😬

So went in for our 20 week anatomy scan!! Everything came back good she has all her organs, bones, toes fingers! Her heart rate was 141! She weighs 10oz! All her test came back negative for Down syndrome and all other test! But the doctor said she is measuring 6 days behind her due date. That it’s most likely because she will be a small baby. Note me and the father are both small with me at 130 pre pregnancy and my boyfriend 150. Has anybody else had them say their baby was measuring behind, and everything okay? Just a small baby??? I’m a first time mama and this is my first viable pregnacy after 2 miscarriages and I’m just really nervous but trying not to stress to hard😬🥴