Congratulations on finishing the box challenge!

You've definitely improved a great deal through the set, both on your line quality, fixing some mistakes you were doing, like wobbly lines, and in your convergences, so I'm pretty happy with it.

To improve your boxes even more, as you still have some problems with a few divergences on the inner corners, you can take a look at this diagram .

Thinking about the relationships between lines, instead of focusing at 2 lines at a time will make your boxes get better, if you aren't doing it already.

And drawing the inner corner first might help to get them better as well, as I show here