168 championships completed

Ive completed all the championships and it says 99.5% What am i missing?

Check your progress tab to see if you have anything missing in there.

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Did that,do u have to own all the cars?

Nope - just complete all events and collect all boards and similar (roads, speed traps etc).

Completing all 168 championships is not the same as 100% game completion.

check bonus boards, speed zones, speed traps, roads discovered, bucket list - and anything else I may have missed.

The Bonus boards against Turn 10 i havent completed is that it?

Yes completing the bucket list (all three) count.