Help !!

So I went to Maternal Fetal Medicine last month @ 28 weeks and our LO was 2lbs 6oz. @ 31 weeks at the hospital I’m delivering at she was 2lbs 11oz . The doctor said it’s a concern because she only gained 4oz in a month, that she’s in the 5th percentile. Today at 32 weeks and 3 days I went back to Maternal Fetal Medicine and the nursed measured her 3 times and got 3lbs 5oz. So my ob wanted to measure her himself and he got 2lbs 12oz which was the same thing they got in the hospital and then proceeded to say “it’s hard to measure her because she’s in a ball” but said if she stops growing completely then they have to deliver her. But my thing is if the 3lb 5oz measurement is incorrect wouldn’t that mean that she been 2lbs 11oz for a month ? That she already stopped growing ? I believe the nurses measurements are more accurate