Spacers are dish, dish is spacers. Either the wheel is dished or it is not.

Did you observe that the frame was actually aligned before you spread it? Presumable that was with a different wheel, and that wheel might not have had perfect dish, making up for dropouts that may not have been perfect.

If the frame is straight and the dropouts aligned, the thing to do to align a dished wheel is to remove a tiny bit of dropout material with a round file. Less than half a millimeter total would shift the wheel 3mm.