Car Accident Today - Long Bike Ride Tomorrow?

Earlier today, I was driving home from a long run at a local state park.  I stopped at a red light and got rear-ended.  Right now, I don't feel bad, but I'm assuming I'll feel the whiplash tomorrow.  Should I still try to do my scheduled 5 hour bike ride tomorrow? 

Here's my dilemma--
I'm scheduled to do my first Ironman distance race at Coeur d'Alene on June 27, so including tomorrow, I only have four long rides left before I begin to taper. 

If it were earlier in the season, I wouldn't think twice about skipping one long ride, but it's late in my training plan and I still have some serious ground to cover before the race, so I really want to ride tomorrow.  But on the other hand, it's really close to the race and I don't want to do more damage to what's already been done.

Any thoughts or suggestions?  If I don't feel terrible right now, is there still a possibility that there's some damage that I'm not feeling yet?  Is doing the long ride a bigger risk than I'm imagining? Thanks in advance for your help!