For the first 50, your lines are overall very clean. I noticed very few traces of arcing throughout the set. Your convergences also show good accuracy, though I did see a few minor instances where lines pair off and converge towards two vanishing points, like box 2's blue lines and box 30's blue lines.

For the next 50, your lines remain clean, though I did see a little more arcing here and there, like in box 57 and box 87. Your convergences also show improvement in accuracy, though there were a few more instances of lines pairing off, like box 56's red lines, box 71's blue lines, and box 97's blue lines.

For the last 150, while your lines are clean, I did see more instances of arcing appear in this set, like box 104, box 190, and box 246. Be sure to take your time and practice the proper technique.

Your convergences show more improvement, though I noticed a more instances of lines pairing off, like box 119's orange lines, box 174's purple lines, and box 228's green 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.

I did note the missing line extensions, but since you already addressed them, I'm not worried. I also didn't see any other mistakes with them.

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