What Does Mucus Plug Discharge During Pregnancy Indicate?

Hello Mam, I am pregnant for 28 week 6 Days....The last 2 days I can see a small amount of mucus plug coming out. yesterday afternoon it was around 3cm long. I dont have any pain in abdominal area. I was having placenta previa stage 3 which improved during 28 week usg. Now it moved 3.64 cm from the OS & turned into grade 2,low lying planenta. I am having complete bed rest since yesterday as adviced by my doctor.He suggested duvalolan retard instead of duvadilan which I was having since begining. reintroduced susten 200 again to be taken for next 1 month & hyocimax 2 times a day. Pls suggest if it all ok? Is there any chance of miscarriage?/ pre term???