The aspect ratio of your image was not proportional to the aspect ratio of the canvas, so like waterscoop said they squished your image down to fit on the canvas.
.... because if they scaled it down to fit, it would have left blank space on the canvas. So yes, you either need to find a canvas that matches the image aspect ratio or do some cropping and scaling yourself to get it to match whatever canvas size is available or preferred for your final product.
The aspect ratio of an image describes the proportional relationship between its width and its height. It is commonly expressed as two numbers separated by a colon, as in 16:9. For an x:y aspect ratio, no matter how big or small the image is, if the width is divided into x units of equal length and the height is measured using this same length unit, the height will be measured to be y units.
In, for example, a group of images that all have an aspect ratio of 16:9, one image might be 16 inches wide and 9 inches high, another 16 centimeters wide and 9 centimeters high, and a third might be 8 yards wide and 4.5 yards high. Thus, aspect ratio concerns the relationship of the width to the height, not an image's actual size.
