The test was never "Everyone should do X" for Kant and he never presents it as such; its always been "It is permissible for everyone to do X" - and then you test the maxim in the universalization procedure. 

In the Typic of Practical Reason, in the second critique, he specifically says that for this test to work you must imagine the action you're investigating to be a law of nature (e.g. if you're pondering whether killing random people is wrong, you should imagine a world where everyone has the natural tendency of killing random people, and then ponder on whether such a world contradicts any of the formulations of the Categorical Imperative).