So long as there are no shifts, then spontaneous magic should generally do what you wanted it to do. The exact effects and manner in which it works may not be quite what you expected. Instead of a bolt of fire that incinerates your target instantly, he may just burst into flames, or his head may melt, etc.
Actually, if there are no shifts at all, the end result should be very close to what you wanted it to be, if not identical.
