Fundal height

I know they aren't really accurate but has anyone had fundal height measurements that are just all over the place? With my first I followed a perfect line all the way through, this baby I measured smaller but normal at my first measurement, the shot up above 90th cemtile at my next then today I measured below the 10th centile? I'm getting a scan on Thursday but I'm so confused how she can go from huge to tiny within 2 weeks 😕