Low hcg

I just had my blood work done to confirm pregnancy and my levels are only at a 46. My Ob nurse called and said that anything under 200 requires a retest in a week. I took letrozole so idk how likely it is that I ovulated late and am just earlier then expected. If my levels haven’t at least doubled by Sunday then it’s not a viable pregnancy. Has anyone else had a similar experience with having low hcg levels and things end up being okay? Trying to stay hopeful here but also really nervous. I don’t want to stress the pregnancy and make things even worse. Any hope would be helpful!