First they look very good for a first grow. Way to go.

At this point all you can go on is the health of the plants. You can weed out the weak ones. However you can't tell male from female untill flowers start. They are just showing phenotypes of parents. Seems like all I see no matter what strain they do this.

Best thing to do is start to flower when you have 4 true sets of leaves. When they proof and show sex then pick out the best plants. The ones that show you the best health and go back to veg and clone away. These will be your mothers. I know it takes more time but in the long run you will more than ketch up. And all will be female without dought.

Hope this helps, I'm shure we will get more opinions. Go with what you feel is right.