I'd be surprised if fertile eggs can be sold in the US without being clearly labeled as fertile on the package. If the word "fertile" isn't on the package, I doubt they are.
We cracked one that was in the incubator for 2 days open and it was clearly infertile. So we are pobably just going to buy some hatching eggs. We will keep these ones for a few more days, but if nothing happens we will just chuck them.