1. Every child is different. For the first kid, you'll often blame or credit your parenting for some of your child's positive and negative traits. For example, our son (oldest), has always been a great eater. Tries all new foods, loves his vegetables, eats healthy portions. We thought it was because of our "baby-led weaning". Then we had our 2nd and she is a very picky eater (better now than before, but still a big difference) and we often struggle to get her to eat enough. Our 3rd is in between the two, eating wise. More or less a similar environment growing up. The other area this comes up a lot is sleep. Some children sleep terribly, others sleep well. Some parents have a few children who sleep well and feel that they made that happen. Some parents have children that don't sleep well and feel cursed. Try not to be too hard on yourself or too high on yourself.
2. They are a lot more durable, and less fragile than you'll initially feel. I stressed a ton over our first child. I tried not to be a helicopter parent, but still, in relative terms, every health issue stressed me out a lot. In fact, I stressed so much during the first weeks of our first child's life that I got stress-induced shingles! For the 2nd and 3rd, I'm much more relaxed and I simply have less time and attention to hover over everything that happens to them. Let them fall, get hurt, etc - they can handle it and they learn from it. Injuries, scars, etc all heal for the most part. Obviously this does not apply to truly serious conditions of incidents, but those are rare relative to your worrying.