HCG blood test for miscarriage

So I had a miscarriage on 12/19. And my doctor told me not to wait to start trying again ( I’m 35) so we have. My at 4dpo. Yesterday my doctors office called and said hey the dr wants you to come do blood work to make sure your HCG is at zero, I said well he told me not to wait and I’m in my two week waiting period so it might not be at zero so what do I Do. So they said well just go ahead and come in on Monday. So my question is what if it’s not zero? Am I pregnant or is is from my miscarriage? I had a period and took a otc test and can back negative before we started bd.