Hey I'm new on Affinity, I used to work on Adobe. I'm not an english native speaker so I hope my explainations are clear...
I used to draw on Illustrator. In this software when you draw a shape with the pencil tool, then you can select it and draw "over" the line to refine it, or extend it. In affinity designer if I draw a curve with the pencil tool above an other curve it creates a new curve, it doesn't change the old one... I don't know if you see what I mean... Is there an option to change that ?
Thank you!