Having been down the road of sonograms for yrs trying to conceive... No, usualy you can not see a heartbeat until week8.
The technician is going to be vague, don't take that as a sign of something being bad. Their job is to do the sono then report to the Dr.
If you had identical twins, they could be in one sack, otherwise you're right, there would be 2 sacks.
If he said it looked right for the gestation, they it should be safe to assume all is ok.
The concern with unusualy high HCG levels if there aren't twins, can be molar pregnancies.
Usualy these end by week 8.
However, I don't know if this can be detected at 6 weeks.
Some people get negative results of pregnancies untile they're almost 2 months pregnant, to me, that says 2 things, either you're off about when you got pregnant, which sounds like you're not since you had a sono, OR you may just have one of those pregnancies that have odd numbers but not necessarily something wrong.
I know it's a waiting game and it's frustrating and it seems like a day takes forever.
There is nothing you can do and although you're just seeking experience from others, patience and deep breathing will keep you relaxed.
I hope to hear some good news in 2 weeks ;)