Put 4 large eggs in a cake calling for 3 eggs - what to do?

Thanks for the reply and just a quick report - I likely was okay on fats and moisture. I did just put extra 2 T regular flour (rest used cake flour) because I hoped it would be forgiving. I suppose I would have added a bit more plus other things. Now it made 6 pans so I have 2 small stack cakes to make. These 6 inch pans I have are really shallow, can't be split. The 'crumbs' recipe for this cake is fantastic. It was a bit salty, but worked with the full recipe. The whole cake is really sweet, too sweet for me to take more than a couple of bites. Other people liked it more than I did. It is sorta cute and homily at the same time.

I have been reading about how changing up a boxed cake by adding an extra egg, milk instead of water and butter instead of oil will make it taste better. Did all three of them and, honestly, I don't notice a difference. Personally, I don't think an extra egg will do any harm.

If the batter is still unbaked, add other ingredients proportionally and save the extra 1/3 batch for another use - freeze or give away or re-purpose.
If you've already baked it, don't know what to suggest :(

I should mention that the cake calls for 2 c flour, 1-1/2 tsp baking powder and contains buttermilk and a bit of oil in addition to butter and shortening.

Also while I am at it, she makes a 1/4 sheet pan and stamps out the 6-inch rounds from a ring. One layer has to be 'frankensteined' together from scraps. But I have 6-inch pans. I guess they will be a bit higher. I will cut them with my 6-inch ring or a knife to expose the sides and show the sprinkles. That should be okay, yes?