Most likely you're running into a very common problem caused by the lab's machine:
"Most labs have their printers set up to increase the size of each image by 1-2%. This expands the image beyond the borders of the paper. The reason is to prevent a white strip from being printed along one or more edges if the paper is not perfectly aligned within the feed path."
From here:
http://www.drycreekphoto.com/icc/usi...r_profiles.htm
(near the bottom of the page talking about cropping)
I've run into it as well and on that site they give dimensions by which you can increase the canvas size of your file to avoid the specific problem. Frankly, this is one extra step I shouldn't have to take and will not have my restoration stuff printed at the lab that did it to me before. The other lab I use hasn't caused any problems for me so I tend to stick with them.