Missed Prenatal Vitamins

I picked up Centrum prenatal vitamins. There were 2 bottles in there and the box said it contains DHA. Perfect! I don't know about anyone else, but my mind has been mush lately!! I guess i just assumed that 2 bottles meant 2 months worth. Man was I wrong :( I am 5 weeks 5 days and it turns out for the past 2 weeks, I have only been tAking DHA and not prenatal vitamins :( one bottle of each in the box. Boy do I ever feel like a horrible mom already. Not starting off too great. I need to know, how bad is this? What are the chances now of neural tube defects? Have I completely f***ed up?! :(