It is for sure your monitor.
You are working with extremely dark values that appears lighter on your screen ( cheap screen? over boosted luminosity? whatever.. ) and what you get is a lack of information in this range ( creating banding ) caused by a low quality screen and the default gamma set to optimize lighter values ( cause the eye sees lighter ones better ).
It is dangerous because your values are wrong actually :/
The problem was solved just by manually dong the gradient with a soft round, it was just using the gradient tool that i got the banding. Someone else suggested to me that i should increase it to 16-bit or whatever, il look to do that next time. I don't really think it was the monitor personally, my monitor is pretty good, and it also looked the same on my vaio and my friends screen. but never mind, its gone now haha
well your picture is still extremely dark so I still think you have something to do with your screen.. unless you'll add brighter values later (?) but the very subtle details you're painting are barely readable actually.