keliru dengan due date.. .

Hi....actualy my lmp is 24th july 2019 sepatutnya due date i ikut tarikh ni 29april2020...nw currently 31 weeks..tapi masa scan kurang seminggu its shown 29 weeks...dari start mmng mcm ni..i tanya dr dia ckp u fllw due date 29 april je...baby growth ok x de masalah....tapi i risau je la....kenapa tunnuk 1 minggu kurang