It does look a bit small but just keep growing it, it seems to have been stunted by something but I can see the set i'm sure they will be okay, at least its not, not growing, the other is looking really good how many do you have as of now, the reason I ask is because depending on how long you plan on vegging, or grow style, you may be able to sacrifice that runted one being that you have a cab like mine, 4 weeks veg=3 plants, 6-8 weeks veg=2 plants, and anymore you can do one huge bush in there, so just take your pick.