"I knew too much."
Translation:Mi sciis tro multe.
I think koni could work here, but it would be a bit awkward and the meaning would be different.
I know we're not learning German here, but this one explains the difference: https://yourdailygerman.wordpress.com/2014/11/26/what-is-the-difference-wissen-and-kennen/
koni – kennen
scii – wissen
I'm not sure if the meanings match 100% though, but I think it's a good approximation.