Both male and female plants have those sharp bits called STIPULES.
They have nothing to do with telling the sex of the plant.
This can only be done once flowering has started.
The you will start to see something form in the area close to the stipules.
Females will have a CALYX start to form and then will push two hairs out of it, this tells you it is female.
Males will have STAMINATE PRIMORDIA form in the same place but they kind of look like little lobster claws, no white hairs will grow out of them.
The one above is too small to sex yet i think...
Unless grown from FEM seeds.
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ataxian I see you are using blue masking tape for training, not sure if the glue will be absorbed or damage the leaf.
I use plastic coated wire and attach to the net pot or even fishing weights to hold the stems in place.