You would need to tell what kind of flour you used for one thing.
Letting it sit for 30 minutes wouldn't give enough time to let the
gluten do its thing. Your first proof should be 4-6 hours or longer
depending on what you are trying to accomplish. Also you don't say how
long you baked your loaf. In short you need to give more information if
you would like more help. Teresa
www.northwestsourdough.com