Not sure if you've got this working yet, but I'll ask a dumb question. Is it possible you have the width and height switched up when you create the image? With desktop stuff I'm used to the longer side being the width, but on phones/tables the longest is usually the height.
Also, make sure you're working in pixels and not some other unit (inches, cm, etc.) in your program. I know I've accidentally done this a few times.