Macbook resolution set at 2560 x 1600 somehow?

Hi, thanks anyway but it's definitely a Macbook. If I click "About this Mac" it says "Macbook (Retina, 12" Early 2015)". And like I said, in the Display area of the System Report it shows the display as 2304x1440. So, on some level it knows that it's a 2304x1440 display. But on another level it's behaving as if it's a 2560x1600 display. I'm quite knowledgeable about computers and macs, but this is my first Retina machine, so I wasn't sure if it behaved differently in some way that I'm not accustomed to. It's as if there's some sort of 'retina display driver' in MacOS that covers all the Retina display groups, and it's selected the wrong one for some reason. Do other 12" Macbook users take a full-screen screenshot and it comes out as 2304x1440?

Just to give an update, I've contacted Apple Support, we went through all the settings, did an SMC reset, NVRAM reset and OS reinstall, without any luck. Could someone who owns a 12" retina MacBook please confirm that what I'm experiencing isn't normal behaviour? I'm at a loss, so all I can think is that it's either normal behaviour or it's some stupid setting that I've got wrong. A software issue would surely have been ironed out by now, and it doesn't seem like it'd be a hardware issue. Or, maybe it's a problem with the graphics card hardware or firmware? I'm pulling my hair out with it, any help or insight would be greatly appreciated!