Re: 4gb of ram
That's not correct, that you would need to fill each slot with the same amount of RAM, or have a stick in each slot.
The OS only recognizing 3GB of RAM, is a limitation of 32-bit software. It simply won't be seen, so it won't damage your computer in any way.
The ASUS guide probably said that, if you're using a 32-bit OS, because 32-bit cannot handle more than that.
All those aside, why are you wanting to put 4GB of memory into your computer? Is it just because you need to have a stick in each slot? Are you into heavy video/photo editing? If not, 4GB is not needed. What is the purpose of your system?
3770K | ASUS STRIX GTX 1080 | DDR3-1600 16GB | CORSAIR 650D | CORSAIR HX 850W | CORSAIR H100 | SOUND BLASTER Z | ASROCK EXTREME4 GEN3