All in all, you've done a pretty good job. I do agree that you had some issues with proportions, though that is fairly common and not something I'd dwell on too much at this point. I do have a few things to point out for you to keep your eye on however.

Overall your adherence to the techniques and concepts covered in the lesson is quite solid. Especially as you push through the exercise, you demonstrate an increasing willingness to subdivide your boxes further, finding more specific landmarks and measurements for each little bit of form information. This results in constructions that feel more and more solid and believable. Comparing your mouse drawings to your egg carton, for instance, the egg carton's much more precise in where every aspect of it goes, whereas the computer mouse is a little more loose, relying on more guesswork to bridge the gaps between determined landmarks.

One issue I'm seeing come up here and there is the tendency to redraw marks that you feel didn't come out correctly the first time around. This happens moreso with lines that curve, but either way, it's a pretty common issue students have, and it generally happens when we loosen our reins and allow ourselves to draw more instinctually rather than continually applying the principles of the ghosting method to control every single mark we put down. At the end of the day, if we're putting a mark down reflexively, that mark did not go through the three steps of planning, preparation and execution - it just jumps straight to execution.

Ultimately we want to make sure every mark we put down is planned and prepared for, because we want to ensure that every mark has a specific job, and that we try not to put down any marks that are not contributing something. It's especially important considering just how many lines we have flying around on the page, between construction, subdivision, etc. At the end of the day, if we make a mistake, or a line doesn't go exactly the way we want it to, it's best to leave it be. If we put another mark down to fix it, we're only going to be drawing more attention to it by piling up ink in that area, and in turn we're giving up our control over how we guide the viewer's eye around our drawing.

Now, obviously this happens somewhat naturally when dealing with ellipses - it appears you've freehanded them, which suggests that you haven't been able to get an ellipse guide. All things considered, you've been managing it quite well, and this is one of those situations where we get additional linework, but we do benefit from it as well (drawing through our ellipses helps us maintain more confident, evenly shaped ellipses). Freehanding them does mean however that we are making the homework for this lesson more challenging, and splitting up our focus between multiple tasks. As a result, we may end up with constructions like your chess piece, where the degree of your ellipses doesn't change in as consistent a manner as it should (though the box itself in which they were all constructed also plays a role in that being off). If you're able to get an ellipse guide before moving on, then I strongly recommend it - otherwise, have patience with yourself, and give yourself a little more leeway in terms of your expectations.

Continuing to look at that chess piece, I did notice that you applied form shading to it. Remember back in lesson 2, I explained in this section that we would not be including form shading in our drawings. The areas of solid, filled black should be focused on cast shadows instead - that is, the shadows we get when one form blocks the light from reaching another surface. These shapes therefore fall on surfaces other than the form in question. Form shading on the other hand is where the surface of the form in question gets darker or lighter based on whether it is turned towards or away from the light source. So, for comparison, this drawing has a prominent cast shadow with no form shading, and the cast shadow helps to separate out our forms quite nicely.

I know that there may sometimes be the urge to add form shading - specifically when we feel our forms don't feel solid and three dimensional enough. Always remember that if a form doesn't feel 3D, it's because of issues with its construction - shading will only build upon that, and won't be able to actually fix the root of the problem.

One last point - I noticed that when you draw the outline of the shadow shapes that actually fall on the surface under the object (to help ground it), you seem to try and draw that shape in a single continuous stroke. This usually results in a shape that is very organic, ignoring any sharper corners. While this shadow shape by no means has to be specific and hyper-accurate, try breaking it up into separate lines, so you can more easily control where you've got straight segments, where you've got curves, and how they all connect to loosely imply the shadow of the object.

With that, I think you're largely doing quite well. While you will want to continue investing plenty of time into observing and studying your reference images/objects, I think your work is coming along nicely. I'll go ahead and mark this lesson as complete.