The pic on the left (from what I can tell) you topped it correctly. I cant see any pre flowers from your pics but by the size of your plant I would guess that it is still too young. Your plant is at the begining of the vegetative state and you should start seeing signs within a couple weeks or so. Light cycle also can delay preflowers. If you veg your plants under 24 hours of light, I have found that when growing from seed the preflowers take longer to show. 18/6 light cycle might help if you are not already doing so.