For the first 50, your lines are very clean. I saw only a few instances of arcing here and there, like box 14 and box 40. Your convergences also show good accuracy, though I did notice some lines pair off and converge towards two vanishing points, like box 9's blue lines, box 25's red lines, and box 44's green lines.

For the next 50, your lines remain very clean, with only a little arcing throughout the set like box 58 and box 85. Your convergences show improvement in accuracy, though I did see a few more instances of lines pairing off, like box 55's blue lines, box 78's green lines, and box 97's red lines.

For the last 150, your lines remain clean throughout the rest of the challenge. As before, there were only a few minor instances of arcing like box 107 and box 210, demonstrating very good technique and consistency. Your convergences also show further improvement, though I did see more instances of lines pairing off, like box 122's green lines, box 176's blue lines, and box 237's blue lines. In these boxes, 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, the pens that you used for most of your line extensions were a bit thick and dark in the photos, which made it difficult at times to see the original lines. If you have thinner pens available, I recommend using them for line extensions in the future.

All said, you did very well. I'm going to mark this challenge as complete.