Did I lose content after I got the writing cube

You have to use the tetromino cipher on the chalkboard.

The answer:

or just press: ↑ ← RT A LT → A ↓, and an anticube will appear

This is the unfolded counting cube. The numbers don't mean anything by themselves, but the cube is meant to associate these types of symbols (portions of a plus sign) with numbers. Seeing the unfolded cube in this 16-cube classroom informs us that this room is about numbers, since it uses the same symbols. Some deduction in this room leads to solving the number cipher.

This is the number cipher giveaway. These symbols are used in various rooms, but they form a Flatland sequence here. (Flatland's conceit is not understanding other dimensions until you can personally experience them.) Without blowing the story, a square protagonist lives in a two-dimensional world, visits Lineland (a one-dimensional world), and later, Spaceland (3-D) and Pointland (0-D). Knowing this, the sequence is fairly straightforward: the numbers represent the dimensions from zero to three.

Likewise, these show three ways of adding to 10, introduce an "equals" sign, show that "three" can be written two different ways, and that a godly squid bequeathed the gift of 3-D.

I don't think this means anything, nor does anyone else. The numbers add up to 64, a prescient number in this game, and when adding the numbers separated by spaces and converting them to letters via a substitution cipher, they spell a naughty word. This game is steeped in apophenia, looking for patterns in static—we don't know if we're being trolled by the game designers.