Help long story

So I’m 28 weeks tomorrow, and my pregnancy has been just compilations all the time, so I’m planning on doing my hospital bag, but what the heck do I put in it? How much of stuff will I need. Midwife has already said baby will be born early bc of my age (16) and bc before I was pregnant I weighed (7 stone 8lb) I also smoke (not as many as before I smoke maybe 3-5 a day compared to me smoking a good 15-25 before) I also have anemia so all theses problems have a percentage that the baby could be born early but with a good 4-5 problems it’s certain my baby boy will be born early.

I’ve had many trips to the hospital aswell as u can tell in my previous posts but Thursday was ridiculous I phoned up and told them my syptoms and stuff (back pain,I already have that as I have a slip disk and also it hurts due to baby ect so it’s always there, this pain would come and go which made my back pains worse and I also had stomach pains ever 10-12 mins and also had my show and reduced movements.) I went to the hospital after they told me to lay on my left side and put a pad on and come in after an hour, which I did and they check bump size and heart rate and she told me to come in when I think I’m dilating and in labour but not to come in before I’m 4cm this is my first child how am I ment to know I’m dilating and I’m in labour??