Hi, which type of ultra sound were you given...internal or external? external scans are usually only meant to be performed 12 weeks on and dont always pick everything up if performed before these dates. internal should be more clearer. Are you deffinately 8 weeks? if you are going by date of conception, then remember that it takes up to two weeks roughly for implantation to occur which could mean that you are indeed 6 weeks? I say take your doctors advice and try to relax because if you worry it will make things worse, and make sure you are taking all the right vitamins! i made that mistake once. hope everything works out for the best for you.
im sorry it does not sound good. you should have seen heartbeat before 8 weeks, however sometimes its not seen early, but with that in addition to you measuring 2 weeks less than what you are...it does not sound too good. go with what your doctor said and hopefully things will work out