HCG levels 46 hours between.

Hello everyone! I got my blood drawn 5/10 and my level was 10 then I got it drawn again today 5/12 and it was 27. I’m not sure how many dpo I am but may have a possibility I am 15-16dpo. The nurse on the phone said that it doubled properly but was still a little concerned that it was low so I have to get it done again Tuesday 5/15. What does everything think about those numbers? Has anyone had low numbers like this early and have had a successful pregnancy? Thanks!