2 weeks isn't much time for any sort of serious training adaptation for an event like that. Also, you don't say what your fitness level is or what your previous cycling experience is like - have you done rides of that length before?
Your best bet might be to try to get in one really long ride the weekend before - 4 to 5 hours if you can manage it. That will get you in the ballpark of how long you'll be on the bike for the 100k - particularly if you've never done that distance/length of time before, it will probably help your body to experience it once ahead of time. Then, don't do too much training the week prior to the race, better to make sure you are well rested going into it.
Also, make sure you manage your nutrition well during the days before the ride, particularly the day before, so that you start out with a "full tank" so to speak. And make sure you take in enough calories during the course of the ride (lots of posts on that subject here on BF) or you may find yourself bonking hard a couple of hours into it.