According all the sense I made of perfective / imperfective aspects throughout this course, I was expecting "Neměl jsi to říct"...
add to the sense you made. the speaker's disapproval of the action being described is often shown by the imperfective, even if the action is all done with and closed.
That is correct, too.
Proc je zde předpřítomný cas pls? A je špatně: You should not said that?