Belly measurements

Slvelaz✨✨ • 👯‍♀️ 1 Ectopic 2 MC 🌈=11/04/19 🤰due10/01/21

Does anyone know how the belly measurements work? I'm 27w Thursday n my belly measured at 30cm? Unless I'm doing it wrong lol? So since I am Technically 26w 5d am I measuring ahead? Just curious how that works lol