by default, a label has its own size and that size fits the size of the label's contents. Therefore, the 'Alignment' property of (node) labels doesn't seem to have an effect.
For node labels, change the 'Size' to another option than 'Fit Content' to see the effect of the 'Alignment'. Text wrapping is available, too, and can be enabled by setting the 'Configuration' to 'Cropping' (stupid name, I know).
Unfortunately, these two settings are not available for edge labels. Please add a feature request for this if you like.