When established on the arc, you can also use single needle tracking to maintain the correct radius. Maintain heading until the single needle has "dropped" to 5deg behind the wing, then turn 10deg into the arc. Continue untill you are done.
Sorry for the vague answer, I can demonstrate it a lot easier than I can explain it.
DME Arcs... not very arc-like eh?
hope the sim went well. Use whatever method your instructor advocates, and that you are happy with. Don't necessarily listen to anonymous people on internet forums (not that welliewanger and myself aren't giving genuine answers you understand - just be careful!)
TTR