It does say 64bit operating system in the control panel
From what you describe, you have 64 bit Win8 installed.
Now, the maximum memory that 32 bit Photoshop can use on a 64bit Win8 system is 3.2GB or about 3276MB, very close to your numbers. So, it is very likely you are running the 32 bit version of Photoshop.
The kicker is that the Creative Cloud installer actually installs both 32 bit and 64 bit versions of Photoshop to your system. However, I dimly recall reading an article (maybe in the Adobe forums?) that the installer also (stupidly) sets the system to default to the 32 bit version (including file associations) even on a 64 bit OS. This means that launching Photoshop via the installer created shortcut or by double clicking on a file now associated with Photoshop (like jpeg, or instance) will cause 32 bit Photoshop to open.
What you need to do is to locate the 64 bit version of Photoshop in C:\Program Files. Create a new shortcut to this version and use it to start the program. Then, load your files and see if the memory utilization goes up (it should). If it does as expected, you'll either have to always load Photoshop via the 64 bit link, or edit the registry to re-associate the files you are editing with the Photoshop 64 bit executable instead of Photoshop 32 bit executable.