Baby m small?

Hello!! So when I got pregnant, and I was supposed to have 6w and 4 days. Baby was measuring 5w 5d... Then the doctor kind of said at 12w that they will going to still have my due date for march 15. I went today at 19 w supposedly for anatomy scan but baby was measuring 18w and 3d maybe. I was supposed to be 19w and 3d so it kind of confirms what they told me at the beginning but now I am

so worried bout the baby just not grow like she is supposed too or something like that? 😔 Has anyone experienced this? Should I be worried? Ty in advanced.