How do you paint touch-up spots on drywall?
A couple of things could cause this:


the original surface was primed, and you didn't use any primer on the patches.  Primer seals the surface, so changes how the surface absorbs paint.
the original surface was rolled, and you used a paintbrush.  Rollers leave a slight orange-peel texture, whereas a paintbrush -- even the brush you used -- will leave a flat to slightly rippled texture.


More coats of paint will help too, but prime it first.