I don't know the recipe you used off the top of my head, I don't know the method, I don't know what temp you set your oven to. I don't know if your starter is healthy or your yeast is fresh. I don't know what flour you used. I don't know what "dense/undercooked" means to you, specifically. Did it rise at all? Did it not rise? What did you bake it in? Do you know that when you follow a bread recipe "to a T", you're not guaranteed good results in the same way that you might be if you were making lasagna? Particularly with sourdough, temperature and time need to be considered as important as the rest of the ingredients.

If you can be about 90% more specific with your question, it'll be much easier to try to help you troubleshoot.