Yeah but your high school experiment has no feedback mechanisms, no oceans, water vapor, volcanos, solar cycles, plants, and so on. You’re also not putting in 0.04% CO2 vs 0.0395% CO2 and measuring anything meaningful because the scope and scale of the Earth’s atmosphere is unfathomably larger.

If you’ve ever owned a Fish Tank or taken High School Chemistry, you’d realize that even in the most simple environments things don’t always add up in a way that seems intuitive.