Are you doing it by eye and just guessing?
To properly calibrate a display, you need a calibration tool. It has to physically measure your monitors color output, which can only be done externally.
Something like the Colormunki Display would allow you to do this.
You can buy it, or you may be able to find one for rent. I own the colormunki Smile which is not as good, but is a bit cheaper.