Hello. Ladies, has anyone experienced this?

Hello. Ladies, has anyone experienced this? Today I had an ultrasound at 21 weeks, everything is fine with the baby, the placenta is perfect on my uterus. But the problem is that the placenta is low-lying. The diagnosis is "low placental implantation", 1.5 mm, and it should be 2.5 mm. Has anyone experienced this? It's scary, the doctor said it might start bleeding.