Welcome to the Prevention Pit 3, where time paradoxes come to play. You're getting close to preventing the inevitable. Keep going!
However, be warned: the fabric of space-time is thinning. The laws of physics are about to get a serious workout.
Next stop: Prevention Pit 4: The Time-Traveler's Tumbleweed
Or, if you'd rather avoid the pit altogether, you can try the Alternative Route.