When can they determine my babes ?

I did an sonogram at exactly 16 weeks and the tech said it "might" be a girl she said shes just guessing she was not sure! i have a girl already and this pregnancy feels tottally different from hers , I am now 18 and im scheduled for a sonogram on the 5 of janurary can i get an accurate result then? was it too early to determine at 16 weeks? PLUS my lil one had his/her legs closed but the tech said she doesnt see a pee pee! lol thanks for reading!