I have felt the same when I had decided to vax my DD and it is still something I think about from time to time - the what ifs? down the track. However when I weighed up the pros & cons for choosing to vax, the pros weighed up in favour (for us). It really is a tough decision to make & one that I don't think most parents takes lightly. I believe your concern is natural and shows what sort of parent you are :-)
If you still feel unsure about your decision, perhaps you need to go back over the pros & cons for your little one. You can always continue to delay until you have done more research or are feeling a little better about the decision to delay vax.

((hugs))