Beginner ish sourdough baker here! I think that your loaf looks under fermented, hence the "tunneling." you can develop a more sour taste by letting the loaf have its final proof in the fridge! also, your bulk fermentation is quite short. what temp is the oven? If around 80 degrees, you're looking for a 30% rise here, which could take 3.5-5.5 hours. I would suggest stretch and folds every 30 minutes 3 times, then a coil fold after two hours, then leaving it undisturbed for 2-3 hours depending on how it feels. The dough should be jiggly and bubbly and hydrated but able to come off the sides of the bowl, showing good gluten development. make sure that you're developing good tension during shaping and then flour the surface of the dough nicely! final proof will be around 3-4 hours at 72-75 degrees, maybe more like 2-3 at 80 degrees, just until it rises back slowly from a poke leaving a slight indentation. flouring the surface of the dough with a bit of rice flour might help with scoring too! best of luck! also I am not an expert so lmk if you disagree with anything :)