18dpo, took hcg test and it was 167, at 20 dpo it was 476. i have gotten conflicting opinions! is this a viable pregnancy? should i worry?

Patience, not worry.: At less than 3 weeks after conception (less than 5 weeks after the official start of pregnancy), the baby embryo is tiny... really tiny. A couple can live life, relax, do other things that make them happy... and not think about HCG lab values. Many embryos are normal and become successful babies. That said, a portion of them are not normal and naturally miscarry. Patience. What will be will be.