I appreciate all your valuable answers, I was feeling great with it, i wasn't thinking about the stain lately, however, i made a second change of strings last week, i removed the plastic from the pickguard i was very careful, i removed the waste of rusted strings and that kind of things, just with a cloth, for the pickups i had a brush nearby, one that I use for my keyboard, just a small plastic brush, really soft, i used for the small places where i can't get in, like the bridge, when I came to this little part between the end of the neck and the pick up plate i gently swept and then i look closer to see if there was no more dirt
And i looked this, i didn't pay attention before i swept, just after, the right extreme isn't on the best finish neither
That really discouraged me.
I know it will be better to try to send back the guitar, but i don't think it would be that easier, since guitar shops made a lot of exceptions for warranty, wouldn't be easy to find the same model i guess, i had a lot of good wishes with this guitar and i don't wanna turn it into a bad dream like emotional wasting process. Besides that i love the guitar, feels great, sounds great, no buzz or any other issue, i post this to know if someone have found this thing on the neck, remind is a granadilla rosewood, i also attached the papers, thanks