Steven JC,
Further to
Aussie Andy's suggestions quoted above, you might find the following little things I created useful.
This is a spreadsheet which will do the actual calculations for you given the wind direction and strength, your airspeed and the magnetic variation. You could of course use your CRP-3 to do this bit, but do that on the ground first, not while you're flying. It's a bit hard to fly, use a whizz wheel and keep a lookout at the same time
Having worked that out, write the figures down as suggested by Andy on
this and take it with you on your flight.
Good luck for your test!