I started my plants late my self and they are still fairly small also. Where I live flowering starts about sept. 6th so the way I see it we got a hole month of veg. time. If your worried about your yield just grow more plants if you can to compensated for lack of hieght, that's what I did.
Marijuana will flower wether the plant is 1' tall or 12' tall, it's all a matter of how much you will get.