Right, well, information like that should be provided upfront so we can offer appropriate help.
Okay, what size screenshots for an iPad do you have?
You could always use a smaller image, like one for the 11-inch iPad, and scale it up to the right dimensions.
Or, you could make an image that fits the 13-inch size requirements but contains the 11-inch image instead. Think of a gradient coloured background with an image of an 11-inch iPad showing your app, and having some text at the top or bottom. Take a look at other apps on the Store, and see what they do with their screenshots.
Topic:
Community
SubTopic:
Apple Developers