There is more to achieving 100% completion in The Amazing Spider-Man than just finishing the story and completing all of the levels. For example, you also need to complete all of side missions. To see which side missions are still open and available, open up the Manhattan map. Please note that not all of the side missions are available immediately. Some missions become available as you progress through the main story. You will also need to find all of the unlocks and collectibles. If you haven't found everything, replay previously played levels to find all unlocks and collectibles. If you are playing on Xbox 360 or PlayStation 3, you can track your completion percentage from the statistics page on the Cell Phone.