yeah it should fill out now that its flowering.. that is an autoflower strain right? you need add details of your grow. a lot of factors go into making a plant grow.. you havent listed anything about your lighting, watering, nutes, temps... if i had to guess you probably need more lights.. looks like your probably growing with cfl?
Its flowering already! What light schedule did you use? It probably got messed up and is why its flowering early! They need to go to an 18-6 or 24 light schedule or it will keep flowering! Now if you have been doing 12-12 lighting its to late and you my as well keep going and it will be just as big as it wants to get!