B, too much red phosphorus in the burning spoon will not affect the experimental results, so it is wrong.
C. Opening the spring clip before the device cools will make less water enter the gas container, resulting in smaller experimental results, so this error.
D. If the red phosphorus is ignited and put into the bottle, if the cork is not plugged immediately, the air in the gas container will escape, leading to a larger experimental result. This is correct.
So choose AD.