Stressing 😓 Heart Rate

My OB sent me for an NST and ultrasound for a cord/amniotic fluid check after baby's heart rate was lower than usual at my 38-week appointment. There was a lot of heart rate variability, which the nurse told me was good, but her resting heart rate was around 115 at times. The fluid level and cord flow turned out fine they said, so I was sent home. A week later, baby's resting heart rate is still much lower than it had been previously (115-130 baseline) and my anxiety about it is out of control. The nurses don't seem to be concerned, however. Is this normal?!