If they are important shots where you used the full area of the pic, just crop it yourself using PS at 4:3 ratio, assuming you are printing 4R. If you are lazy to crop, just ask the printer to print full print, but that will leave you with 2 borders at the shots ends.
Tell the shop you want to "Fit-In". But if the image has a different aspect ratio from the print size, then you will get some white borders. For me, I prefer the white borders to having parts of the image cropped off..