You won't be able to tell the gender this early. You can't tell if it's male with the naked eye until it starts flowering. If you get yourself a hand microscope you can tell once the plant gets to about the 5th node (set of branches off the main stem), then you look at the V where the latest node joins the stem, you'll either see a blob/blob on a stick (male) or a pointy thing with 2 feather-like hairs coming out (female). If you wait to flower, males are dead easy to spot, they develop hanging pollen sacs that look like little bananas. If the plant aint growing, could be a runt, or could be your reflector is not pointing the light right, or it could be a nute deficiency. Even in the best seeding compost, you still need to start feeding the plant when you water it after a fortnight or so. Could also be root rot - you're not overwatering are you? - my latest lot of plants are about 3 weeks old and I've only watered one of them cos it's huge, the moisture in the soil from when you germinated shoud do for the first few weeks - too much moisture in the soil will rot the roots (what compost you using, most potting compost needs to be mixed with perlite for drainage).