Viral infection

Hello, FTM today I’m 35+6 weeks i had a ultrasound done today. 2 weeks ago i had a ultrasound done and everything was fine with my baby today at the ultrasound they found fluid around the my baby’s heart. She said this can be caused by a viral infection. The schedule me a echocardiogram on Monday but rn I’m worried. Has this happen to anyone? Was there also a misdiagnosed?