FigJam is a digital whiteboard, take advantage of this! Create blank sections that you intend to use a a whiteboard to write on with the digital marker. Unlike writing on a physical whiteboard, these notes are effortlessly captured within the lesson, within the context of the flow of the lesson.  Press M to switch to marker and start writing on the canvas.

Tip: I create additional sections UNDER each section specifically for utilizing the whiteboard feature. This allows me to flexibly go from my pre created text and images I am displaying to writing additional notes.