Rucita, I think perhaps I can do a better job of explaining the idiom "jumping the gun" -- all levity about small Walther pistols aside.
The term comes from footraces, and it means "starting too soon" -- jumping out ahead of the sound of the starting gun; not only not the right thing for you to do, but it messes everyone else up somewhat also.
What is your native language, Rucita?