Orange, I know how it feels. It's always the waiting time that kills. But do take note, for amnio, you will need about 2 weeks for the results to be out. If you want fast (the term called FISH), you can opt for that. Not sure, how much yr side will charge you extra. They can give you results within 3 days.
The scan is not as accurate as amnio. Amnio is almost 100% accurate. For the scan that I'm going, it's actually more like the 20 week detail scan. More detailed and they look for soft markers for any abnormalaties in the baby as well as the bb's organs. For amnio, they are based on chromosome abnormalities.
Don't worry about the pain. It's quite minimal. Just that, make sure after you have done yr amnio, have bedrest for the rest of the day. Don't carry heavy stuff and walk too much.