8:55 AM, Friday April 30th 2021
If you haven't already, read this short article on the topic written by drawabox: https://drawabox.com/article/ink/notpencil. If this doesn't help I'd suggest continuing in pencil or getting in contact with the drawabox team. The rest of this reply will be my own opinion.
With incorrectly placed lines or ellipses, if it's slightly off I'll estimate where the proper line/ellipse would have been and place the rest of the lines accordingly. If way off then I just draw the correct plcement of the line/ellipse in its place.
If you did this course perfectly without fail, you didn't need to take this course. We can't learn if we're right, as we've already learnt it. we learn by correction of mistake. If your making mistakes AND correcting them properly your doing it right. Now this can be done in pencil, though if you rub it out you've 1. wasted time rubbing it out (if the objective is only to learn, not to make it look good) as the time spent literally using the eraser isn't spent learning, 2. removed the ability to see where you've most commonly went wrong in previous studies. Again, this is only my opinion on the topic, so I'd suggest do what suits you best!