concerned :/

so im 29 weeks this weekend.... i had an appt yesterday. everything was good but this whole pregnancy i have been measuring about 4 cm (sometimes more when the students do it) behind on my fundal measurement (its like measuring tape on your belly). anything more than 2 cm off is concerning. she didnt act too concerned but we are doing an u/s in 2 weeks to make sure everything is okay with the baby. i was fine yesterday but today kinda concerned. im sure its fine b/c im a small person but im still worried. i dont want anything to be wrong with bullet or not have enough fluid. even though things could be just fine, please say a little prayer for us. thank you.