New guy from Canada saying hello and needs help!!

Hello folks new guy here!! While hiking I unfortunately stepped on a mallard female sitting on her clutch which resulted in her death . I carefully took what good eggs remained and put into my homemade incubator about a week or 10 days ago. They all looked great when first candled but yesterday I noticed one has a dark spot developing under the shell. My wife kids and I are hoping we can save at least one egg and give it a chance in life. Any help is appreciated!!!!