For the first 50, there are a few lines that arc or wobble a bit, like box 16. While your conergences show improvement in their accuracy throughout the set, I noticed the odd line veering off in the wrong direction, like box 37's orange line. Some lines also pair off and converge towards two vanishing points, such as box 11's blue lines, box 30's red lines, and box 43's orange lines.

For the next 50, while there's a little arcing here and there, like box 63, your lines show improvement. I also see further improvement in your convergences, though there are still some cases where lines pair off, like box 79's green lines and box 94's orange lines.

For the last 150, I see further improvement in the quality of your lines and accuracy of convergences. There are a handful of errant lines, like box 130's yellow line and box 158's green line. Some lines still diverge in pairs, like box 129's green lines, box 180's yellow line, and box 230's purple lines. In these boxes and the ones mentioned above, the inner lines (green and orange in this diagram) diverge instead of converging at the vanishing point. Keeping in mind the angles of neighboring lines can help when planning the box's construction.

As an aside, box 45 is missing an orange line extension. It's not a major problem, since your line extensions were otherwise fine, but I wanted to mention it for future reference.

All said, I'm going to mark this challenge as complete.