I assume you only used the flesh and not the skin/seeds? In which case I would say you should be fine, as this is what I do with my baseball bat zucchini. But the best test is just to taste the shreds and see if they taste bitter to you!

Enjoy your zucchini baked treats!
Susan

I did not peel them, but I did get most of the large seeds out before shredding.

Well as long as the skin wasn't too tough for your taste, I still think you're fine. Especially since your plan is to use it in baked goods, where the zucchini is amost untraceable in the final product.

Here is a link that might be useful: My favorite Chocolate Zuccini bread recipe