28 week scan, measuring small?

So I had my 28 week ultrasound today and the doctor said baby is still measuring small at 2 pounds 8 ounces which is apparently 12th percentile. She said everything else looks good and it could just be that she’s a “small baby”. My belly is measuring normal for this time. I’m confused because I thought this weight was in the normal range? I’m not sure where the 12th percentile came from. Can anyone relate or provide insight?