It’s true, it’s only 2gb detected.
If there is more ram assembled in hardware it is maybe a wrong configured compiled bootloader. Android shows 4gb?
You only can check with your seller if he will replace the box. But what I know 2gb are more than enough for CE.
Chinese box vendors like to fake real ram size by hardcode it in Android. Maybe it’s 4gb assembled but the bootloader is configured wrong so only one bank get detected. So they fake the ram to fix it what in real does only cheat the user. He get 4g but he can use only 2gb.
Anyhow it is ridiculous. They have built a box with 4Gb of ram which is the most expensive part after (if after!) the CPU and they lost themself in making a proper bootloader and tweaking android to show 4Gb!
There are some different Android images out there for this box. Try them and maybe you are lucky and get a working bootloader showing all 4GB of RAM. Or you send it back and try another (not soooo cheap) hardware or even better on hardware of the vendors supporting CE.
On the end of warranty period you need to prove a faulty RAM to them. This is kind of hard and depends on the seller if he accept it or not. Better is to use the 14 days, or is it 30 days to return without any reason - if this option is still possible.