We've had to deal with them twice in two kids. Each time it started as a small red spot/birthmark that was raised and clearly different than a freckle. I believe they say they can grow larger during their first year, and then slowly will fade and break up. Eventually it will recess back into the skin and become flesh colored - not even leaving behind a mark.
I have a child who is now 1 1/2 and it is still red, raised and visible, although it does seem to be slowly reducing in size. Ours were on the scalp/neck area. Have NEVER had any problems or issues.
I have heard of some children who see specialist due to them growing and affecting vision, but I don't know how common that really is. I believe then they are treated with surgery, as a last resort.
You did nothing wrong. It's not preventable or really even treatable. It's just a "birth mark". The red color is indicative of a hemangioma, as are the blue veins. You may notice them more when the baby is upset or tensing up for any reason.
It should completely go away by age 3.
Congrats on your new little one. Enjoy him and take lots of pictures.