the possible causes are,
-blighted ovum: where only yolk sac
will develop without embryo development
-missed abortion: in which case fetus died inside the sac,
wise gestational age
is correct, may be you calculated wrong dates.
now you can consult your doctor and take her opinion regarding this,
if she advices you to wait for 1 more week,
she will kept you on tablets for stoppage of bleeding,
if she thinks first two possibilities she will advice removal of sac.