You can certainly improve your strength and train your body to finish stronger in the 100. Again, you're just going to have to do some longer sprints in training. You can still continue to run shorter sprints, like 40s, to work on your start, drive phase, power, etc. But a couple times a week you should be doing 100s, 150s, etc. Again, take plenty of rest in between each repeat so you can get the most out of each sprint. You don't want to slow down significantly over the course of the workout, so keep that in mind when determining your goal times. It's not going to help if you're crawling by the end of the workout.
If you're doing 6-8 x 100m, a realstic goal time for each rep might be 17-18 sec for your first workout. But instead of blazing the first 50m and crawling to the finish line, try a more conservative approach and finish strong (and focus on maintaining proper form). When you come off the start line try to accelerate with control instead of mad-dogging it like you're running from a werewolf. Keep your head down and lean forward in the drive phase. Lift gradually. You shouldn't be standing fully upright before 30m.
And yes, creatine might help. If you're cramping you should drink more water. Creatine users who don't drink plenty of water often experience cramps. I don't prefer to use creatine because you tend to have significant decreases in strength when you stop using it, but it would almost certainly help you finish stronger in workouts and races.