How many zones does Sonic Mania have, in total?

The ones I have noted are:

• GHZ: Green Hill (from Sonic 1)
• CPZ: Chemical Plant (from Sonic 2)
• SPZ: Studiopolis
• FBZ: Flying Battery (from Sonic 3&K)
• PGZ: Press Garden
• SSZ: Stardust Speedway
• HCZ: Hydrocity (from Sonic 3&K)
• MSZ: Mirage Saloon
• LRZ: Lava Reef (from Sonic 3&K)
• MMZ: Metalic Madness
• OOZ: Oil Ocean (from Sonic 2)
• TMZ: Titanic Monarch

I haven't been able to progress farther. Are there hidden zones? What am I missing?

Solution 1:

Sonic Mania has 13 different zones. (8 remastered, 5 new).

1. Green Hill Zone (GHZ) - Sonic 1
2. Chemical Plant Zone (CPZ) - Sonic 2
3. Studiopolis Zone (SPZ)
4. Flying Battery Zone (FBZ) - Sonic & Knuckles
5. Press Garden Zone (PGZ)
6. Stardust Speedway Zone (SSZ) - Sonic CD
7. Hydrocity Zone (HCZ) - Sonic 3
8. Mirage Saloon Zone (MSZ)
9. Oil Ocean Zone (OOZ) - Sonic 2
10. Lava Reef Zone (LRZ) - Sonic & Knuckles
11. Metallic Madness Zone (MMZ) - Sonic CD
12. Titanic Monarch Zone (TMZ)
13. Egg Reverie Zone

Egg Reverie Zone is the thirteenth and true final Zone in Sonic Mania. It can only be accessed while playing as Sonic after collecting all 7 Chaos Emeralds.

You can view all of the available zones through the unlockable level select menu in Debug Mode.

Source: Sonic News Network - Sonic Mania Zones