8 weeks or 10 weeks ??

Masa 10 weeks saya baru first time daftar utk buku merah .. saya mmg confident tarikh last period (first day start period is 5 oct 2019) sebab habis nikah and sanding , malam tu saya period , jadi mmg ingat sangat tarikh tu. Baru ni bukak buku merah , doctor scan size baby menunjuk kan baby baru 8 weeks , padahal sepatutnya calculation is 10 weeks .. sampai dokter anggap saya salah date period ? padahal mmg normal flow period (tak penah ada problem ) Does anyone ever had this kind of experiences ?