Pregnant again right before miscarrying

Hello ladies first of all I'm sorry if you've ever experienced a loss... This is probably a silly question, but I can't get it out of my head. I naturally miscarried at home at 11 weeks and 6 days on 8/19. I was still experiencing pain and saw an OB on 8/23 where he used clamps to remove the sack. My blood hcg levels on the 23rd were in the hundreds. Yesterday the 30th I went back in and my levels are at 24. I've been barely spotting and I'm afraid I won't get all the way down to zero (test again 9/5). My questions are is it possible when we did the baby dance on 8/15 the day I started to bleed could've gotten pregnant again before actively miscarrying? Why do we have to wait and try when the levels reach zero? Has anyone experienced their levels never reaching zero? Any questions you can answer would be greatly appreciated thank you!❤️