it's a myth that if you don't eat enough your baby will suffer. the baby takes its nutrient from your body - what you eat goes to you. babies born during the ethiopian famine still had an average birth weight of 6-1/2lbs even though the mother was skeletal.
definitely clean up your diet - you don't want to infect the baby with chemicals and preservatives and crap like that.
ease off on the sodium - it can hit your blood pressure - and the caffeine (which builds up in the baby at far accelerated rates than adults because it takes their kidneys so long to process it).
according to your ticker, you're well within a healthy weight for your height so you can be comfortable packing on a few throughout your pregnancy although keep in mind that when you're "Eating for Two", the other one isn't another adult, eh?
OH!!!! folic acid!!!! start knocking that stuff back now! it's vital for healthy neural development.