I'm a mother of 2 boys, 2.5 and 3 months old baby, during my pregnancy I was really anxious about the reaction of my big son. A nursery teacher suggested buying him a baby doll to familiarise him with all the work that a newborn needs.
I did it but didn't seem to work. After I had the baby I spent a week in a cousins house while his dad told him I was still in hospital. i went home with the baby and I was really amazed that there was no bad reaction, actually everything was in my mind.

Don't worry take it easy and everything will be fine