Alright, the only reason I'm telling you this is because i was in the same situation, and after 2 days, I couldn't figure out myself.
I got this from a tip of a friend of mine who did get 100% because he did one thing:
Find and complete EVERY jump in the game with the SAME car, without SAVING in between jumps (i.e. NO getting out of the car once you start to process!)
That was the only thing he did that I didn't do. Once i did it, my percentage changed from 99% to 100%, and you'll see a great hidden message on your stats! <img src="/images/graemlins/wink.gif" alt="" />
NOTE!!!: there are THREE HIDDEN JUMPS (i.e. they don't necessarily appear as the usual ramp)
easy to figure out though after you've been playing the game for any amount of time.
good luck, let me know how it goes.
B---