Slow rising hcg

Hi I am looking forward any feedback or anyone who has anything similar-

My last cycle started on the 14 feb I had implantation bleeding 27th Feb had a positive pregnancy test on the 1st March. Did first blood HCG on the 2nd March confirmed pregnancy was some where in the 400’s then did next blood test on the 6th and HCG was 712 gynie said it was a sub optimal rise in HCG next blood test was yesterday and was 849 so less than a 20% rise.

Went to see gynie today to check if it was an ectopic which he said didn’t look like it which was a good sign he saw a small sac from one angle in my womb. (It’s still very early and hard to tell.)He said I am more than likely going to have a miscarriage but said that miracles can happen. So now it’s just a waiting game. He is sending me for more blood tests on Thursday to check HCG again.

Has anyone has a successful pregnancy with slow rising HCG I am not sure how I feel right now??