Magkaibang Ultrasound Result

Mga mamsh, 40 weeks and 1 day n q ngaun as per LMP. Pero since hindi pa nahilab tyan q, ilan beses n dn aq nilagyan ng gamot to open my cervix everytime my OB examined me for IE. Jan 2 is supposedly my due date pero i had my biophysical ultrasound. It says im only 36 weeks. Mejo worried aq since it does not match sa mga date ng unang ultrasound q. Bka ma overdue c baby. Filed my maternity leave last dec 14 tz from jan 2 to jan 29 due date q. Sayang dn 1.5months. Does someone experience the same? Safe p kaya?