When printing anything you want without a border add around 5mm to the dimensions as a bleed for starters. so i'd increase the size slightly in any case. Crop and cut to the final dimensions as you need, this will avoid white showing were it's not ment to be.

There shouldn't be any need to scale in photoshop at all if the document is set up right in the first place. It actually sounds like the printer is cropping the edges. Is any of the artwork being cropped or cut off at one end. If this is the case check your printer settings in the OS dialogue and check if there is a margin setting or a Borderless printing option. This may .

BRETT