Really great stuff so far! Your organic studies of the trees and roots look fantastic. Also great job on all those cube rotations.
For circles and ellipses, have you tried ghosting the lines a few times first before committing to them? There is a good exercise for them if you make a table with a bunch of horizontal rows and then draw the circles one after the next touching the top / bottom of the grid lines and then just touching the sides of each other. Thereβs an example on my forum page if you want to use it.
I find drawing those digitally is sometimes harder for some reason. If you train for a while with it and still have problems you could download https://lazynezumi.com/ which slows your pen down and gives you more control.
Good luck with your studies!