Congrats on finishing the box challenge! First off I wanna say I love the colors you picked for extending your lines, and your line confidence is awesome, so great job on that! Overall your boxes are pretty solid. But here are a few things to keep in mind so you can keep improving:

---Extending lines far enough

You have a tendency to not extend your lines far enough, and because of that, they are sometimes not enough to tell you where your mistakes are. So when extending your lines do it all the way through, don't be afraid of lines colliding with other boxes.

Also it seems like some of your lines are extending in the wrong direction, this is a pretty important one so I'd recommend looking at this: https://drawabox.com/lesson/250boxes/1/wrongdirection Essentially the lines should always go towards the vanishing point. The majority of your boxes were fine, but there were more then a few that were the wrong direction, so be careful about that.

---Divergences and parallel lines.

Sometimes some sets of lines in your boxes are parallel or even start to diverge a little. Remember that in 3 point perspective; lines will always converge and get closer, even if it's just a little or barely noticeable.

---Hatching lines

While hatching lines are optional, I would strongly recommend doing it in general as it helps convey how your box exists in 3D space more clearly i.e. it makes the front of the face box clear which by extension helps with understanding the box's orientation.

---Lineweight

I couldn't tell if you had lineweight contours on most of your boxes because of the extended lines, so I'll just share it just in case. The contours help clarify your drawing to a viewer and to solidify how your box sits in space. Maybe check this out: https://drawabox.com/lesson/250boxes/1/lineweight

---Similar orientations with boxes.

You have a lot of variation to your boxeswhich is great! But there are still a couple patterns I see you falling into.

I recommend checking out this picture: https://imgur.com/Kqg6uMX. It has a lot of different box orientations. Keep in mind though that the aim of the box challenge is to draw from imagination, not from reference, so don't straight up copy them.

---Inner corner

Finally, the inner corner. It looks like it's still giving you trouble by the end of the challenge, and that's completely normal. Here are a few things that made tackling it a bit easier for me.

First, try this order for drawing boxes.

https://imgur.com/FGdtVwm

Second, you could try to think about relationships of each line on a set instead of thinking of pairs will make you make better guesses. It's explained on this diagram.

https://imgur.com/8PqQLE0

Additionally, in the I noticed you were using the backsides of already printed sheets. It's awesome your reusing paper helps the environment and is fiscally smart, but it made some of your boxes a little hard to understand especially in the ~185-227ish range. So if you can try to get blank paper, or reuse paper that doesn't show on the other side. Not a huge deal tho, most of the boxes I could see pretty clearly.

Advanced exercises

Overall, nice job! Generally your boxes are pretty solid; your line confidence is especially good. Additionally, Once you get more comfortable with the inner corner I recommend looking into the additional exercises here: https://drawabox.com/lesson/250boxes/2.. Good luck on lesson 2 and keep up the good work! :)