The styles provided in the tutorial are just a starting point, you can use CSS however you like to make something custom just for you 
I made the choice to move the post content area to the left so the table of contents nav had space on the right hand side. You’ll notice that if you reduce the browser width in the layout you have made the table of contents will get cut off by the browser window, or wrap under the content.
As for the h3 headings, they get revealed when the h2 immediately above them has been clicked. You can see this happening in this gif when “Working with images in posts” is clicked:
Either that or you don’t have enough content under the heading. The collapsing feature can be turned off in Tocbot by adding collapseDepth: 2 to the configuration. More into on the Tocbot docs: