I accidentally put semisweet chocolate instead of unweetened chocolate in my cake! What can I do? Not enough eggs to start over

I think both Nancy and Adam's suggestions are great, clintonhillbilly!

If you have it, I suggest a sour cream topping with a little vanilla, an a little less sugar than normal. You may also have some luck dusting it with cocoa powder. If you saved a UFO from it ( cake dome), test your fixes using bits of that and taste it before deciding what to use on the cake.

I'd recommend baking it off as is and adjusting after the fact -- does the recipe call for frosting or any icing? Leave it off and opt for something less sweet instead, like cocoa or powdered sugar or fruit. Or, serve it with some simple ice cream instead.

If this is any help, semisweet chocolate has about 15g sugar (1 tbsp) per oz, where unsweetened chocolate has none.
I would bake the cake and serve it
a) in very small pieces
b) with no frosting (don't add more sugar)
c) with clear tea or black coffee, to cut the sweetness
d) maybe with some kind of dairy topping with no added sugar, again to cut the sweetness.
Good luck, and please tell us how it turns out.

Hi clintonhillbilly! Unfortunately baking is a finely tuned beast, and adding/altering the recipe at this point probably wouldn't be a good idea. I'd suggest baking it as is, and maybe serving it with a tart dairy like a dollop of creme fraiche to cut the sweetness a bit.