There could be a few reasons why your cornbread dressing turned gummy. One reason might be that you used too much chicken stock, which made the bread absorb too much moisture and caused it to become soggy. Another possibility is that you didn't bake the cornbread long enough, resulting in a dense final product.   Finally, it's possible that the ingredients you used didn't mix well together, which created a clumpy texture. If you want to avoid a gummy texture in your cornbread dressing, try using less liquid, baking the bread for longer, or mixing the ingredients more thoroughly.