This quick list is for those who may have forgot about what is needed in order to attain 100% game completion on Sonic 3D Director's Cut:
1.) Complete all zones and acts.
2.) Collect every Chaos Emerald.
3.) Complete all Time Challenges
This as far as I know got me to 90% and then there is one final thing needed:
4.) Attain a total score of 5,000,000.
also get all of the continue icons.