Here are some more hints without giving it away in full:
4 is part of the debug world "Chowdren" which can be entered from a secret room in the main menu
5, 8, and 9 are reachable from the main menu
6 is the save station you encounter when walking the path below the infinite darkness to the hidden fairy city
7, but without the rightmost screen of your labeling, is part of The Interlude. The map tells you how to reach it
10 is reachable through a hidden path from (23,20) in chapter 3. The entry spot might be obvious, but getting there requires advanced bouncing skills
11 is reachable from one of the adjacent screens and is actually part of the world surrounding it
12, including the screen above which you labled as part of 7, is an Interlude secret
13 is an Interlude secret as well, reachable from one of the adjacent map screens
14 is reachable from the screen above through a secret passage in the right wall
15 is the only real secret of chapter 1. Getting there requires quick reaction after you've left the temple where you stole the 2 candlesticks