Mamakin,
I would second FFF's comments. I wouldn't want to contradict your instructor as that just adds confusion. However, something to keep in mind if you haven't been taught it. Unlike FFF the technique that reduced the workload immensly for my CPL was to maintain my PLOG on the chart, not the PLOG. By that I mean I wrote my ETA and ATA as well as fixes and times at fix on the chart as I went along.
As described above, again for the CPL diversion I was told to freehand the line. You then align your pencil with the wobbly freehand one and transpose to the nearest VOR rose to get your magnetic track, then just use the common rules of thumb to calculate your heading. You then turn on heading and mark an X with the time (two digits) as and when you identify your position. Estimate your course correction and proceed. It works beautifully.
My advice is don't fall into the trap of getting into inflight calculus. Your thumb is about 10nm, just count thumbs to get the distance. Just think of 100kts as being 1.5nm/min. Use the straight edge of the pencil to guess a 10 deg drift line to estimate your heading correction. Simple.
It is very satisfying and liberating being able to go aloft and navigate very accurately with just a watch, a line on the chart and pencil.