AMD stock cooler is bad, however it can spin to very high RPM like ~3000 making alot of noise, thats why ppl hate it, however that fast speed should make your setup alot cooler.
Please try alternative sensors :
speccy
hw monitor
CPU-z
BIOS
And make sure, then please make sure you assembled the computer parts properly especially the cooler and thermal paste area.
I dont belive 50C idle is normal, not unless you live in Africa, cause that means at load it uses ~70C - 80C
Are you overclocking ? if so then this is okay/
Make sure the CPU power saving tech are enabled, and your CPU should go down to 1400Mhz or something when its idle is that so ? does it still be 50c cause to me thats abit too much
Make sure you CPU fan header is attached to 4 PWm header and 3 PWM header