voltage divider confusion
1) Wall warts are very inaccurate and there is a high chance it is not supplying exactly 6 volts.

2) Don't forget that resistors have tolerance. I can almost guarantee your resistors are not exactly 220 ohm and 1k ohm.

3) Voltage dividers really shouldn't be used for power supplies because the "regulation" will depend on the load. If you attach a load, it will combine with the resistor divider network, changing its output voltage. 

It would have been more helpful if you had attached a diagram to your post showing exactly how you have things connected.