I did my NT blood tests & scan and my AFP blood test & u/s at a Fetal Diagnostic Center. When I was giving blood, I was worried about a new type of test they were doing and if they got enough blood. She said that the blood test was a very small percentage of the whole equation. She said the MOST important things are the markers and measurements. I hope you can rest knowing that your odds are fantastic and if not the only rest you are going to get are with the amnio. Just to throw this out there too though, the perinatologist said that he delivered this month a full term downs that was great blood and great measurements. There is a 2% chance of that too. (just telling whomever reads this post)
Please keep in mind that the AFP is just a screening test. A "positive" result does not, by any means, mean that there is something wrong with your baby. All your other tests have come out fine, right? If you truly don't NEED to know, as you said, then just pray for the best, relax, and enjoy the rest of your pregnancy. But, it sounds like you are pretty stressed out. You may want to consider the amnio just to put your mind at ease so you can enjoy the next four months. It's definately a personal choice, and one you and your partner need to really think about. Whatever you decide, good luck! Keep us updated...
Tricia