Hi Doctor Whe. I Had First Ultrasound They Told Me

Hi doctor Whe. I had first ultrasound they told me i m 6 weeks and 6 days pregnant and they didn't see fetal heartbeat and they booked me for next internal ultrasound after 2 days but again they didnt hear the heartbeat. And after 2 days i was having spot but wasn't heaving bleeding as periods. And i went to the hospital and they did again the ultrasound but still they couldn't find heartbeat. Now they booked me early pregnancy clinic . I am really scared please advice me as soon as possible