What should my HCG Level Be?

So I am 4 weeks and 6 days pregnant today from a FET. My first HCG level was 160.6 at 9 days past transfer. My second HCG level (3 days later) was 512.2. My doctor was pleased with these results. Now they want to repeat my HCG test one more time 8 days later after my second beta. What “range” do you think my number should be 8 days later? Has anyone else had their levels checked again about a week later? I’m just worried cause I had an early miscarriage before and it has taken 3 years since to get to this point. I just want to prepare myself! Haha