Open world games such as AC: Origins utilize the CPU much more then a linear game so it's not surprising to see such a high usage. Go into the task manager and make sure only necessary programs are running (nothing extra like Discord, Web, Netflix, etc). Then, just to make sure, I would do a full scan with Windows Defender & Malwarebytes (Free).
To increase your GPU usage you'll want to increase the graphic settings and if that doesn't get it near 100% then use AMD's VSR (virtual super resolution) which will increase the resolution of the game then scale it back to your native resolution. This will make the game look a bit better. Note that this will increase your GPU usage but may not give you smooth FPS.