Answer
Signazon.com always measures height by width (H x W) in inches. When you select size on the website, height is always the first dimension, not width. Make sure this matches with your file size. If you saved in width by height (W x H), the image may look sideways in the proof.
Another reason could be that your image was saved horizontally or you have an invalid rotation applied. You need to reopen your image file in the native design application (such as Illustrator or Photoshop) and rotate it until it is vertical. Resave the file, and try to upload it again.
If you are unable to fix this issue, just explain the problem in the “Order Notes” box on the payment page. Our art department can adjust your file and send you a proof for a $25.00 design fee once the order is placed.