100 km/h?! Get a paralegal on that one. An experienced agent would be able to get that witness's evidence tossed. Can you recall if the witness was driving substantially below the speed limit at the time?
A lot of people overestimate things when dramatic events occur. Example: Last year, there was a two-car crash on my street (actually - 3 or 4 times a week there's a crash on my street but that's a different matter). Pontiac turned left in front of a Cadillac, he broadsided her and spun the Pontiac around. Speed limit on my street is 60 km/h. Witnesses estimated the Caddy's speed at between 80 and 130 km/h.
(Yeah, right, if it had been 130 km/h, the Pontiac would've been cut in half and she would've been dead.) I later found out (actually witnessed the thing go to court, driver who turned left fought her charge of Left Turn - Not in Safety, claiming the Caddy was going too fast), Toronto Police Traffic Services determined that the actual speed of the Cadillac was 71 km/h. Maybe the same eyewitness bias thing happened with you...?
Did the officer take any measurements to determine your speed (skid marks, impact damage), or did he rely on the eyewitness statements? Do you know if he took photographs? My suggestion for the time being is to go back and re-visit the scene of the collision. Put together some notes, if you haven't already. Also keep copies of all of the paperwork from the shop that fixed your car. The more information you have showing that you were driving well under 100 km/h, and much closer to 50 km/h, the better it will be for you in court.