My Instagram is not using the whole screen on my iPad.

Instagram make an iPhone app with a fixed aspect ratio. On an iPad you may have an icon the will shrink or enlarge the display, but it might not use all of the available canvas. This isn't a fault with your iPad, or Apple, but a conscious choice by the developer not to build in as much flexibility for different screen sizes as iOS is able to support. Send your feedback to Instagram.

tt2

Maybe I'm wrong then, I don't use Instagram often, but it is still down to the developer to keep up with the impact of any changes Apple make to operating system services on the performance of their app. On the iPad I see it as a scaled up version of the iPhone app rather than an app designed to use the larger screen fully when it is available.

tt2