To add to what bird said, a few things:

-Fill your page with boxes. Keep them the same number, but make them bigger. Don't worry if the extensions collide with other boxes.

-Most of your boxes are done with extreme perspective, keep in mind that you should be practicing more the shallow perspective ones as they're more useful and important, so focus on them on your next warmups.

-On the ocassions you use hatching, you do it a bit rushed. Place the pen carefully at the sides of the planes of the boxes you want to hatch so there is no fraying on both ends.

Now about the inner corner issue you were mentioning trying to draw boxes on this order might be helpful (It was for me).

The main thing that will help you to improve your inner corner is to start thinking about the relationship between lines over a set. It's explained in this diagram.

Thinking about the complete set of lines instead of thinking lines in pairs will make your guesses more accurate, which will in turn make the inner corner better, so try to start thinking about it.

Good luck in lesson 2!

Here are 2 guides https://pastebin.com/dYnFt9PQ on lesson 1 submissions and on https://pastebin.com/dbjR9MFj critiquing box challenge submissions, if you choose to critique others. Just like with this one, if you don't get feedback or just want it faster, do 5 critiques of lessons you've completed, and reply here or ping me on the discord, I'll critique one of your submissions.