Deep breathe and write out specifically what you are missing.
I have 'completed' the game as well but the only chapter I have a 'missing hat' is in the final chapter, which I call 8-4. (Book 7 part 1 & part 2 just get confusing to me. In all my notes book 7 part 2 will simply listed as 8.)
First thing to remember when you look at the chapter is how they break down. With the hats there is one hat given for True Wizard then however many hats are in each chapter.
7- 2 Forest of Dean Lake- that are 4 hats, 1 brick & 5 characters
7- 2 Malfoy Manor - Nothing
So 7-2 Forest of Dean - 4 hats
Regular play
1) in the water near the large crab
2) In the forest- lead the fire crab to the embers on the right side. It will ignite the embers which will melt the ice around the hat next to it.
Free play
3) In the water- Dark Magic on lock of container to the left after you crash through the 1st layer of ice
4) In the forest- use Hermione's bad to get the mushrooms, to bounce to the upper ledge. Use a strong person to open the tree and the cat to walk up the tube to get the hat on the upper limb.
* "5th hat" is from True Wizard
8-1 Hats
Regular play
1) Deluminator to move the light from the goblin vault to the high cup holder. Jump to the platform.
2) Not entirely sure if this is one or both but In hogsmeade destroy all the Harry posters / message boards.
Free Play
3) In Dragon room- Dark Magic on red objects. Levitate them into place. WW sticky wall at the top
4) In the vault- Strong person on back door
* "5th hat" is from True Wizard
8-2 hats
Regular play
1) In the chamber- Spectorspecks, redact
2) In the chamber - Purple spell each set of snakes teeth to lengthen them
Free play
3) In the fire room saving draco- the first place you can stop after you have grabbed the broom. Destroy everything you can. A hat will be in one of them
4) In the fire room saving draco- There is a vault at one of the places to stop the broom. Use a goblin.
* "5th hat" is from True Wizard
8-3 hats
Regular play
1) Apparation point- Apparate hat is right there
2) Boat House- Fill the water machine on the right...spits out a hat
Free play
3) Courtyard- Put out all the fires
4) Courtyard- use Hermione's bag to put out a fire (I think.)
* "5th hat" is from True Wizard
8-4 People
Bella, James Potter, Lily Potter, Molly and Voldemort.
Which person are you missing?
That was my quick version. Let me know what specifics you need from here.
Joy88