/ic/ - Artwork/Critique

I know you guys get people posting fucking circles here all the time, but I am going through Brett Eviston's Art and Science of drawing because I want to get back to the basics and while I completely understand the idea of a volumetric sphere having two lines that bisect it at a 90 degree angle and two ellipses that go along those lines and that the degree those ellipses are determines where the center line is on that sphere, I am having a hard time conveying that.

Firstly, I feel like my circles in the bottom right lean to one side? Like when you flip the canvas, they appear lopsided even though I am not trying to make them lopsided. They all lean to the right. Is this even a concern I should be having or does it really not even matter that much?
Secondly, for the ovals I can not for the life of me get one side of the ovals to appear darker than the other, I always fuck it up. Is this an important skill? Applying pressure at different points in the ellipse to make it appear darker/thicker?
Thirdly, because I can't get one side of them to appear darker than the other through applied pressure, the spheres in the top right don't look very good.

Do you guys think this is just because I am doing this digitally? Am I using the wrong brush? Should I break out the charcoal pencils and newsprint?

Again, I hate to bother you guys by posting a bunch of fucking circles that look the same as any other circles and asking for help, but hopefully you can help with these specific questions. Always appreciate it. Also, I resized the image, I didn't actually draw them this small.