31 weeks and 1cm dilated😬

This is my 3rd ptegnancy but my 2nd baby thats made it to the 3rd trimester. My previous pregnancy i had my son at 36 weeks exactly. I went in for a tegular check up they checked my cervix i was 8cm n they sent me to L&D i didnt feel contractions til i was 10 cm n ready to push. I was mostly having back labor n didnt even realize it cuz it felt just like back pain. Well now im 31 weeks with my 2nd son n i got checked yesterday and im 1cm dilated 50% effaced and my cervix is soft. The midwife said she even felt the babys head when she checked me.(i asked her to check me because with my other son i was 4 cm at 34 weeks) idk if im gunna have my son early again or if ill be going full term (i doubt it). Im just so nervous it being so early and im dilating and having really bad back pain that wont go away and lots of pressure in my pelvis. I dont want to go into labor rn or so early. My other son was born n was almost 7 lbs n didnt have to be n the nicu but i have no idea how big this one is. Im just so worried he wont be big enough if hes birn early. Any other mommas been dilated early n made it past 36 weeks? I did with my previous baby but it felt different i didnt have back pain or pressure with my previous pregnancy until the day i went into labor. I feel since hes so low and im 50% effaced n my cervix is soft n hes low ill go into labor sooner then 36 weeks. My other son wasnt low n i wasnt egfaced when i was 8cm. Its so different this time. Any advice?