Lil Help on my Durban Possion

Basicly i have had her in 12/12 for over 3 weeks and still no show of pre flowers!!!!! Any1 help me quick as im going to kill it!!!!

Theres two possible reasons.

1. Durban Poison is a Sativa and VERY long flowering time (13+ weeks)
2. You have light leaks in your grow room not allowing the plant to get full darkness (not actually in 12-12)