Shorten cervix at 18/19 weeks , please help😔

Kl

So i was having a check up and my cervix measured 33mm(which happens usually after 35 weeks) , it was closed and firm tough.. Doctor didnt point any alarms. I know cervix should be 40-50mm at this point and now im scared to death of premature birth or another miscarriage. Do you ladies have any experiences on this, what were your cervix measurements, what did you do and how did it go? Please share your story