5w3d Transvainal U/S shows only sac... Doctors Worried!

Hi. Went for an early transvaginal U/S yesterday.  Thought I was 5w3d, but I only measured 5w0d and the doctor made a big deal out of it for it being only 3 days.  We only saw a sac with nothing in it. I'm really not sure how they claimed nothing was in it because she was only looking for about 15 seconds.  The nurse called back this morning claiming my HCG was 4080 and that if it was a viable pregnancy they should've seen something yesterday.  The rescheduled me for another set of tests monday afternoon and said if we don't see anything then they would like to terminate this due to the risk of an ectopic.  This woud be my 4th MC and 2nd ectopic in a row since July.  Honestly I'm a little worried, but I feel totally fine unlike the last ectopic! I think it was just too early to see anything! My husband is freaking! What are your thoughts?