First off, you should have used a solvent & your fingers to take of the TIM. Goo Gone works great.
But since you've scratched it, start out with 320 or 400 until you can no longer see the scratches. Then go to 600, 800, 1000, 1500, & 2000.
That will put a mirror finish on it if you take the time to do it right.
Viper GTS