results help

hello im pregnant with my 3rd baby due november,i went for my rountine bloods and scan at 12 weeks 5 days im now 23 weeks. the results came back as having a 1 in 15 chance of having a baby with downs syndrome i was offered amnio but decided not to have it .im looking for some help with my results from blood tests ,hcgb 103ng/ml ,nt 2.700mm ,papp-a 3331mu/l. just wondering if you can explain them to me ,my 20 week scan showed baby was healthy and no problems with organs or growth. Thank you .