Ok so you thought a branch was a preflower...it happens.
You can move forward and throw some big ass lights to your little seedlings and they will still be able to make some magic. Usually after about four weeks depending on many variables you should see preflowers. Those are the white hairs people talk about. Before the hairs even protrude you can see either a club-like nub if its a male or a slipper looking growth at or about the fourth node of growth. I have some closeups of a few preflowers in my past grow logs on here, and there are others if you search the forum using preflower. If you read thru the previous links above regarding FAQ and Basic gardening you will get the run down.