Possible po ba na di match sa lmp yung ultrasound?

Sabi kase ng ob ko 6-7weeks preggy daw ako if bbasehan last menstrual period ko, nung nagpaultrasound naman ako sabi nung nag ultrasound very early pa daw mga less than 4weeks pa lng daw . Then nung binigay ko sa ob yung mga test sabi nya lahat ng test sakin is normal except sa ultrasound kse bkit daw very early pa ( 0.71cm gestational sac) . Sabi nya something is wrong daw so pinapabalik ako for ultrasound again after 2 weeks. May makaexperience na po ba sainyo nun ? Please sana po mapansin ninyo. I am really worried po. First baby po pati namin to