That's the difficulty, probably, the aptitude bit. Either you have it or you don't. And since it is something that you cannot do anything about, you really shouldn't be afraid of it, but just accept it whichever way it goes.
The fact that you show a lot of interest and motivation will already get you quite a way towards your goal.
I've heard on numerous occasions that with an infinite amount of time and money, anyone can be taught to control aircraft. This would however not make you an air traffic controller, because that requires a skill set that either you do or you don't have... which is also why there is a set limit on the amount of time you can spend in each stage of training.
No amount of preparations for feasttests and similar will give you this skill set, and if they don't notice the lack of it during the interview, it will probably get found out quite quickly during training.