Measuring 6 weeks 3 days at 8weeks 6 days pregnant and an irregular gestational sac. have had brown spotting but stopped now. what's my prognosis?

Not good: if you are really 8wks, 6 days should have been able to see a fetus with a ht beat and even if you were really 6 weeks 3 days can often see a fetus with a htbeat you most likely have a missed AB can confirm for sure by doing repeat US 1 week form the last one your provider should have already told you all of this

Wait and see: It is very difficult to predict outcomes with early pregnancies at the stage that yours is in, until bright red bleeding, cramps and tissue passage occurs.