Yes, you know you'll worry. You see that your mom and grandmother worry. Others will tell you that you'll worry. But you won't fully experience this wonderful worry until your child arrives.
The minute you hear his sweet cries for the first time the worry starts. This is gut-wrenching love. This is beautiful worry.
Poop- this is something you'll read in every parenting blog, every static site devoted to babies, every book, every forum. You will experience lots of poop. It will not bother you. Breastfed baby poop has been described as smelling like yogurt or buttermilk. What will really worry you about poop is when your tiny tot stops pooping. Parker didn't poop for like 4 days. Of course, being the Google goddess, I learned this must be because he was dehydrated. My RN mother-in-law assured me continuously that he wasn't dehydrated. This is when I learned about Karo syrup in his bottle.
Genitals- If you have a girl, you'll have better luck with this (assuming you are female yourself). However, if you have a boy, you'll be totally confused by your son's penis for the first 3 months, at least. It took about 3 weeks before I was completely convinced that Parker's circumcision would eventually heal. After this, a weird cheesy, fibrous matter started forming under his foreskin. Didn't seem to bother him, but it certainly bothered me. Then my pediatrician chided me for NOT pulling his foreskin back to keep it from growing back! Growing back?! Is this really an issue?
By the way, your husband/boyfriend will be no help with this. Just because he has one, doesn't mean he remembers anything about it at this size.
Belly button/umbilical stump- I was terrified that the child was going to develop an adominal infection. I kept an eagle eye on his tummy for any trace of red marks. Chris caught me sniffing Parker's belly at least six times a day. I worried he would go to kindergarten with an umbilical stump. Then it fell off and he bled. And I cried. It doesn't matter what amount of blood comes out of your child-- at that stage, its always a big deal.
Breastfeeding- I attempted this... It was not enjoyable. I did not feel bonded with Parker during feedings. It was not magical or calming, or any of happy/joy words that the Boobie Police use. It was hard, and caused me to dread meeting the needs of my child. Not good for me or him. (If you breastfeed, I'm impressed and awed. I do wish it had been a better experience for us.) Parker did not associate breastfeeding with food. He was a large child, and we supplemented from Day 1; so he was not a fan. He was hysterically hungry, and screamed at me for letting him starve. It was devastating. It did not last long. Then the guilt of not being able to breastfeed set up house, and stayed for a few weeks.
Update: P is now 10 months old, and the above issues have been resolved... or at least accepted.