Paint color not matching, why?

I painted a room with Berh Sandpoint on top of Berh white #75 Primer. After noticing some bad areas, days after it was done, I decided to fix those up by sanding, priming and painting over. But now the color is darker and the whole thing looks worse because there's a darker patch.
So my question is, is there a technique for matching repainted patches the same color as I have painted the room?
Why is the color now darker? I have stirred up the paint good before painting to make sure that it wasn't settled.
If I can't fix this, I'll have to redo the whole room.
Any help/advice is appreciated!
Thanks, --PhB
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snipped-for-privacy@hotmail.com wrote:

second coat made it darker....
sorry you will probably have to repaint.
if you need more than i container of paint buy as needed then mix all containers together
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