i forgot to add all the sugar to my banana bread anything i can do with it now that is is done

Depends how much sugar you put in, but you can probably salvage it. I halve the sugar in the banana bread recipe I use and it's still sweet. You can also top it with frosting.

Similarly to BerryBaby, I would either soak it in a caramel sauce in some fashion, either through a poked hole method or literally just soaking it in a caramel sauce. Or, turn it into banana bread pudding!

Using a long skewer poke holes all over the top of the bread.
Make a glaze-1C sifted Powder sugar, 2 T milk. Hand whisk until smooth, gradually pour over bread making sure it gets in all the holes.

and when in doubt, smear some peanut butter on a slice and call it a day!

How much did you leave out? If it's less than a quarter of it, just roll with it, you may find you like the less sweet version anyway. Sometimes these experiments were just meant to be.