Percentile and weeks

Emily • 29, Loving Wife Mommy to Abrielle 💖 7/28/16 Mommy Again 2/19/19 💙💖
At my 20 week appt they told me that my baby girl is in the 93rd percentile. 😱 I was 8.6lbs, and my MIL said all her babies were 7.3-7.8lbs. 
Obviously super nervous about my natural pregnancy now haha
How often from appt to appt can this change? The midwife didn't seem concerned, but she's not the one pushing this kid out! Haha