First of all, Congratulations Baby Pike

I understand how you are feeling at the moment. I had a similar experience. My pregnancy wasn't planned either. I actually never ever wanted children, and I made that clear to everyone around me. The idea frightened me a great deal.
I was absolutely shocked when I found out I was pregnant, and I also didn't believe it because I have Polycystic Ovaries.
When I found out I was 9 weeks pregnant I was surprised because I thought I knew I was 4 weeks! I wasn't sure if I was going to keep this baby because I was absolutely scared out of my wits!, but as soon as I saw my little bubs on the screen and her beating heart ,when I went for my dating ultrasound, I knew I wanted to keep my baby. Even though things around me were not ideal I knew I would make it work somehow. Baby Pike, if you listen to your heart you cannot go wrong. Trust your feelings. That's what I did and now I am so so grateful. And things will seem less scary once you start learning more about your pregnancy, and you will. There is plenty of wonderful information out there

Don't worry about how your diet has been and that you haven't been taking folic acid etc. My diet wasn't the best before I found out I was pregnant and my baby is perfectly healthy. It's never too late to start, so like a few other people here have mentioned, drop by your local chemist or supermarket and pick up a pregnancy multivitmain. I use Blackmores Pregnancy Gold.

All the best