Also contact Richard Heaton on this forum if you need help.
Don't worry so much about remembering formulae, but get smoking on the flight computer! There are many questions you can answer without making any calculations at all. Remember that the Nav exam is not a nav exam as such, but a maths exam using navigation as a backdrop. Referesh the principles of isosceles triangles, memorise the cosine for 60 degrees and the sine for 30 degrees (both 0.5 - why do you think 60N or S is used for many questions? Because the departure is half).
Good luck
phil