I would try the larger paper too. Sometimes a cover might be able to physically fit on a smaller piece of paper, but your printer might not have the ability to print that close to the edge. If you use the larger paper, that issue should go away.
For example, I can print PS2 covers on letter size paper, but it barely fits. A different printer might not be able to print that close to the edge, so even though a PS2 physically fits on letter size, some printers might require legal size to make it fit.