If i was you i'd do the test the way your instructor taught you. The time to develop your style will come after you have passed.
Think about it, if you start doing some islands in 3rd, some in 2nd it's another decision you will have to make and in your test the last thing you want is to be indecisive. If you go round in 2nd when 3rd is OK the worst that will happen is the car will go round a bit slowly. If you're in 3rd when you want 2nd at best the rounding will be juddery and you may do something that causes you to fail.