If you actually literally did that, then I think Colin should have given you full marks for Q1 since the only difference between what he wanted and what you did

If you actually literally did that, then I think Colin should have given you full marks for Q1 since the only difference between what he wanted and what you did was terminological. (Personally, I would write O(2^n) = O(3^n) but would not say that O(2^n) is equal to O(3^n). Which, yes, is rather weird.)