Microsoft word 2007 problem with setting margins on label?

I am making a custom size label on MS word 2007 and I can't seem to set the margins. I put in the size of the label and when I put in the margins to center the address 2.5" from the top and 1.5 from the side it tells me "margins, labels size produces a page that is larger than the label page size" When I take the margins out it lets me create custom size label and then I "eyeball" where I want the type to fall. This works but seems crazy not to be able to set margins. I looked at MS web page and it just said to make sure that the label plus the margins don't exceed label size. I don't want them added together, just want to set margins.