Longer response questions requires you to know your content very well and apply it. Might be a good idea to do a few extended responses and read the marking criteria, it'll really help to show where you get your marks from.
I'm pretty sure you cannot get good marks if you write your creative on the spot, unless you're some freaking genius. Even authors and writers write many drafts before they publish their work.
Real hard to get 99+ from now. 99+ is all about dedication and consistency in your work ethic. And also you shouldn't be aiming to high if you think you cannot really achieve it because you're just putting a lot of pressure on yourself.