You are still in your first trimester, and the dose of Dong Quai (Angelica Sinensis), as you say, is well below therapeutic ranges, and far, far below "high" or problematic doses cited in the literature as a concern. In my estimation, you have nothing to fear about the little you took with the prenatal vitamins. Still, I agree with you: switch to a prenatal formulation that does not contain Dong Quai or other unfamiliar herbs, though, just for the record, nettle leaf, raspberry leaf, and other nutritive herbs are generally considered safe, even recommended by some midwives, during pregnancy.
I re-checked the literature on Dong Quai and birth defects. There is one report, questioned by health experts, of one woman taking an herbal combination of several herbs including Dong Quai that may or may not have been a co-factor in her baby's birth defects. Of course, we want to know more. I am sad for her experience. The good news for you is, there is no other research linking this herb with similar problems.
As I scan governmental, medical, and popular sites, I see a fair amount of fear of the unknown reflected in the blogosphere, not supported by either scientific or traditional information, about Dong Quai acting as an estrogen (it does not), and as a blood thinner (to some degree, but not significant in the amount you were taking). Occasionally, Dong Quai may even be prescribed for a pregnant woman if she needs it.
Most healthy pregnant women on prenatal vitamins do not need it. So, rest assured, it is extremely improbable the amount you took did much of anything. Still, stopping the vitamins containing Dong Quai is my recommendation. I also recommend you give yourself credit for researching this, asking the right questions, and taking the safest, most cautious path for your peace of mind, all important to you and your baby. You have my best wishes for a safe and happy pregnancy.
Yours, Amanda McQuade Crawford