Does anyone else feel like that his when trying for baby?

Today we’ve decided to let it happen when it does for baby 2 and my son is nearly 2. Today we started trying and I’m on Day 9 of cycle and realised there’s a 10% chance of this happening and now I’m not sure if I want this. Now I’m terrified incase this one of time works. I do want another baby but he would only be 2 years 9 months and is still a baby himself. He won’t be at nursery yet by time baby came if it did happen. Are these normal feelings? But at the same time I want them close in age. Why do I feel so muddled up?