Congratulations on finishing the 250 boxes!

Just like you say, your boxes are a bit stiff. This is because you're trying to focus on accuracy over confidence.

As mentioned in lesson 1, it's more important to draw confident lines than accurate lines, and because of this, you should strive to draw confident lines always, even if they miss the end mark.

Here's a text from lesson 1 that explains what I'm saying

Also worth thinking about is the fact that there are several levels of "success" with this exercise:

Level 1: Line is smooth and consistent without any visible wobbling, but doesn't quite pass through A or B, due to not following the right trajectory. It's a straight shot, but misses the mark a bit. Level 2: Line is straight, smooth and consistent without any wobbling and maintains the correct trajectory. It does however either fall short or overshoot one or both points. Level 3: Line is straight, smooth, consistent without any wobbling. It also starts right at one point and ends exactly at the other.

As you can see, a line with wobble will be level 0, it doesn't correspond to any level. So a wobbly line, no matter how accurate, will always be worse than a confident line, in drawabox.

You've however applied the line extension method through all your boxes, and drawn them pretty big, which is really nice, so I'm only going to make you do a few more boxes, 5, just to make sure you understand how to make a line confidence, by sacrificing accuracy.