Oh.
My.
God.
Not.
Again.
A search using words like, oh, I don't know, maybe "world championship" brings up these, among others:
problem starting Gran Turismo World Championship
Beginner and Professional Race list ??
Can't enter GT World Championship
GAR! Problems entering World Championship
Help!
Won't allow entry into World Champ
Why can't i race?
Pro events - GT world champ - not accessable!?
OK, I'm tired of cutting and pasting URLs, you get the idea.
Not to mention it's in one of the stickies at the top of the page.
The most common failure is mistaking bronze for gold. They are practically identical on most TVs, show check your diary.
Next, win championships, not just all the races. If it's a series, you have to win as a series.