First rule of growing is: never get attached to your plants , you will end up hurt.

Okay, well you know, males happen. There are a million more seeds so don't get dicouraged and try again. But, unfortunatly, you can't change the sex of a plant, to my knowledge anyways.

But, if you do get a male, I wouldn't grow the whole thing out. I would chop it as soon as it showed and start a new seed right away. The male plant has very, very, very little THC in it. So what most people do, is chop it down and throw it in the hash bin for when they do a next hash or oil run. But trying to get THC from just 1 male plant would prove to be a waste of time. Male plants don't orduce buds, they produce pollen sacks containing pollen, that contains no THC.

To be 100% sure of the sex of your plant, you have to wait until about 2 weeks into the 12/12 cycle. That is the only way it will show its true sex. Also, when the plant is mature, it will show you pre-hairs, but I find they can be misleading at times and find it's best to wait until 12/12. Mature time varies for different strains, but mature is full grown veg, maximum veg time.

You can switch to 12/12 whenever you want. But you have to remeber that the plants size at the end of 18/6, will double, some evenb triple in height by the time it's done flowering. So if your plant is 10inches when you decide to switch to 12/12, it will be approx. 20-30inches by the time it's done flowering. Look at your height restrictions and do the math.

Good luck.