When you plot a nondimensional raster image, such as BMP or TIFF, the size of the plot is specified in pixels, not inches or millimeters.
Each plotter has a maximum printable area determined by where it grips the paper and how far the pen shuttle reaches. Verify that the plotter is capable of plotting the new dimensions.
The program prints a cross that defines the paper size and a rectangle that defines the printable area. If all four sides of the rectangle are not printed, increase the printable area.