Commit to the mistake. Ultimately mistakes are expected - but the mark is on the page, the decision has been made, even if unintentionally. Keep pushing forward with it as is.

Mistakes are unavoidable and part of Drawabox is learning to work through them and create convincing images. In my view that means that the box still has to be a box, with lines meeting at corners. Don't write it off as a failure, think about which compromises will result in the most convincing box.

Here's a recent post showing that even with a ruler it's not possible to get the lines 100% accurate, but they're still very convincing boxes: https://drawabox.com/community/submission/3STUM6V . Don't think you're expected to create perfection when drawing freehand. Focus on being as accurate as possible when drawing your lines then do your best to work with whatever is on the page when planning subsequent lines. The better you do at the first part the easier the second will be.

I would say either scratch it ( which I did occasionally ) or make the best of it but don't try to correct lines you have already drawn. Let the perspective checking lines guide you to where you went wrong and learn from it. Move onto the next page of boxes.

First: good luck with 250 boxes challenge. It also took me more time that I expected. The worst thing you can do is trying to make the 250 boxes on a row under 2 days... The best way to tackle the challenge is to draw between 25 and 30 each day (or 2 or 3 days each a week) and putting concentration each time you're making a box.

You said that you miscalcul a line. It's not necessarly a bad thing, it means that you try to put a marks for a construction line.

You can some line weight to make a constrast between the body of the box and other part of the line.

If you feel your first line is incorrect the best thing to do is not to use it. To make your submission sheets clean, it may be even better to use another paper sheet and keep the one with the line (and or shitty boxes) for another use.

Just like when you write a kanji, the order of the strokes is important. I strongly recommed you to draw your box by always putting the marks on paper in the exact same order. When you "draw a box" in 3d/ with three vanishing points, you need to start with a Y shape. The upper part of the Y will be the top of your box and are linked to vanishing point 1 & 2.

Be sure that the left part and the right are not perfectly equal else you'll have only three line instead of one. After you drew your Y shape complete to get a flat square (the futur top of your box).

Finally choose a 3rd vanishing point. It will be linked to the bottom of the former Y shape. This VP need to be rather far away, else you box will be distored but not too far else it will pass on 2D mode.

Good luck with the challenge.

This is a great question & so glad you asked. I am just beginning the Challenge, and I think my question relates to this one so I'll add it here. Thank you to Eric Na for creating the tool that generates box corners to use as starting points. My question is: does the tool generate corners of actual, rectilinear boxes, and I don't have to add any length to any of the sides as presented? If I were able to copy each prompt exactly (not going to happen -- that's just in a perfect world), and I completed each prompt "correctly," would I end up with a perfect, rectilinear box? The reason why I ask is because, even using the prompts, my boxes are terrible. They are never rectangles with squared corners. Is it just that I need more practice, or is it that I might have to add length to some of the sides as presented? I'm only about 20 boxes in, so I suspect that I just need more practice. Thank you for listening!