HCG hasn’t doubled in 48hrs

So

Has anyone experienced their HCG not doubling in 48 hours and still had a viable pregnancy? I’m estimated 5w 1d and mine was supposed to reach 66% but only reached just over 50%. Its baseline was 2,349 and the nurse said it has gone up to 41,000 but i don’t get how that would work if it hasn’t doubled, unless this number needs to be converted into something? I have to have bloods redone in 48 hours and if they haven’t doubled by then they’ve told me I need to decide what I want to do next about the pregnancy…