What paint and what color did you use? How did you do the touch-up? Sometimes a touch-up spot can be darker but lighter is a little weird. Problems can happen with deep tone colors.
I recommend using the same application method for the touch-up as was used for the whole wall. Example- use a roller instead of a brush. Make sure the paint is well stirred.
You can also try polishing the spot with a clean soft flannel cloth. Sometimes this will help blend things together.