I have a question about syndactyly. What did I do wrong?

Nothing! Syndactyly, or fusion of the fingers or toes is one of the most common limb malformations and nearly always an inherited condition- this is a minor and fairly easily corrected malformation which occurs in otherwise totally healthy kids. This is not a result of something mom or dad "did'! http://www.Ncbi.Nlm.Nih.Gov/pubmed/22333904.