You have to add LayoutData to the Label.
This Data object is basically consisting of some constrains, telling the label how to look.
Label oLabel = new Label (parent, SWT.NONE);
GridData oGridData = new GridData ();
oGridData.widthHint = 50;
You should think about a generalized implementation if you need it more than once (e.g. to get all labels look the same).