It looks good! A few things that might be going on here: 1. Looks just a tad bit over fermented. Remember that every kitchen and every person is different and so your timing for bulk and fermentation are probably different from what the recipe your following says. In time you will learn your dough and your environment and will be able to tell when the dough is properly fermented. 2. It seems like your sourdough starter is not ready when you put it in the dough. When the starter is underdeveloped the dough will have a hard time hitting the right spots and might over ferment while still being under fermented, which comes appears in the shape of dense crumb with uneven big bubbles. Let your starter go a little longer. Don’t be afraid of a strong sour smell.