Thanks for writing to us with your health concern.
Generally the cardiac activity becomes visible at 6 weeks itself by transvaginal ultrasound
At 8 weeks, it should definitely be visible.
Yes, the rate of growth of the gestational sac
is also worrisome.
Visualization of a fetal pole
is slightly reassuring, hence you have been given the benefit of the doubt by your doctor.
As there is no vaginal bleeding / spotting or pain with cramps, chances are high that you might go on to have a normal pregnancy
there is no other option but to wait for 2 weeks.
IF there is no heartbeat by then, this is definitely a failed pregnancy and you would require termination of pregnancy.
if there is any ominous sign in the interim period, then see a doctor at the earliest.
Till then try not to worry, as it will negatively impact the pregnancy.