Does my class measure how good a player I am?

No. The IWBF says class reflects functional capacity to perform pushing, pivoting, shooting, rebounding, dribbling, passing and catching, and it does not measure skill level.

Trunk movement and stability during these actions are the basis for class assignment. Classes are defined by "volume of action", meaning how far a player can lean without holding the wheelchair before losing balance. Classes 1 to 4 are recognised, with 0.5 values for borderline cases and 4.5 for the player with the least disability.

Source: iwbf.org/the-game/classification/.