Golly, that is a big egg!
Though that doesn't mean that it is fertile.
There is only one way to know if it's fertile - incubating them.
If you have an incubator, continue to incubate the eggs, whilst turning them at least 3 times a day - Then at around day 7 or 10, candle the eggs or do the float test on them. If there's a chick inside, it means it's fertile, if not, then you can eat it. (Unless you have a broody hen to incubate the eggs

)
For the float test, if the egg floats and bobbles around, it's fertile, if it sinks, it's not (I think that's how it works ^-^)
Otherwise, if you've seen the male mount at least one of your females and you know for sure that that's her egg, then there's a high chance it's fertile.