Honestly this might contradict what I suggested you just now, however don't get too worried about the rushing or not thing , I've also been suggested a bunch of times that I rushed an exercise or a lesson in general.

I believe that it is best to just keep in mind that you can take things slow and also take several days to complete one exercise... If you feel like it.

Truth be told, I usually too get the urge to "go" and wrap things up, especially when many weeks have passed since I started drawing a lesson's exercise, I think it's only natural.

So as long as you feel satisfied of what you did, I'd say it's good enough, if it isn't then somebody will tell you to re draw some pages, no biggie.

About the hatching lines, Uncomfortable did say to hatch, however not like that in the rotated boxes exercise, in his youtube video he hatched in the "gaps" between the boxes, or better yet the sides of the boxes.

I don't think he has actually stated that hatching the front plane of a box is wrong in that particular exercise, however for me personally it was a bit distracting ahahah, so maybe is best not to do it.

Anyway I wish you a constructive and pleasant artistic journey!