My Plant already in preflower?

Yep, identifing its sex.....female. In future, if you are after decent yields, grow photoperiod fems and then you can control when flowering occurs and only when YOU are saisfied with the plants size. Autos are not all they are made out to be and probably not the best choice for new growers using normal/average equipment. Flowering in earnest is still 2-3 weeks away, so don't switch to bloom nutrients until there are small tufts of white pistils/budlets forming, as cannabis still needs adequate nitrogen (as found in grow formulas) during early flower.

you have a preflower, yes. those can develop in vege. if it is a photoperiod, it's not in flower until you give it a long enough uninterrupted dark cycle (and continue to do so). typically this is 12on / 12 off, but many plants will work at 14/10... even a rare plant may flower in 15/9, but you douln't want to bet on it, lol. 12/12 is safe to avoid outliers. if it's an autoflower, that's a good sign to guesstimate flower phase started about 7-10 days prior from the time you have a well-fromed preflower. This stuff doesn't grow overnight.

Yes

When our plants mature they begin to show signs of their sex, in which the pistols confirm this is a female plant. This means that the plant has matured and is ready to flower. Of coarse, you do not have to flower now if you do not want. Congrats, it’s a girl 🤣 Hope this helps.