the SG I would definitely think even at 3 months old if it were a boy it would have wattle growth already. with it being an SG and no beard, the wattles coming in would be obvious. I am fairly sure thats a girl.
all my silkies have spur bumps, they get them around 2-3 months old, just a tiny bump almost reminds me of a pimple. lol And my silkies all chest bump and fight too, my hens are meaner than my roosters are sometimes!