A few things you can try:
1) Select everything>deselect everything>select everything>try to export.
2) Cut the image selecting everything
3) Make a new image with the desidered dimensions,make a new layer and fill it with color,then open the .psd file as layer (open as layer or just drop it in)
4) Load the .psd with Gimp then export with it.
If you reach point 4 and you don't have gimp,you can give me the .psd and i'll try for you
Last resort option: Cut the image off the screenshot