The photo is not very clear, so the egg looks 50%-50% to me.
I’d keep the egg and try to incubate it anyway, there is no hard doing it. I've seen hopeless eggs hatch in my own collection. Just when you gave up hope and just left it to "sit" there with the others, it hatches at the same time as other eggs. If you are lucky it may be fertile and can survive. However, corns do lay clutches of at least few eggs and, in addition, this egg has been left abandoned for a couple of days as you mentioned. Then if you or your snake moved or turned it, embryo would have drowned as well. Your chances are little, but…
I’d also try candling it. Place a small torch (like a pen type) against it and see if you notice tiny veins inside the egg. If yes, the egg is definitely alive, if not, give it several days and try again
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It’s always easy to throw the egg, but let’s give it a chance and a good try. You know what I mean? And I’d bury it a little deeper in the substrate, 50%-80% deep.
Good luck.