Do you have a butane lighter? I don't know exactly how much you should take. Two hits of 15x made me trip pretty hard. I imagine if you take one moderately large hit you should trip.

If you take a little too much it's not going to hurt you. Just make sure you have someone sober nearby in case you start getting up and walking around while tripping. One of my friends took three hits of the 15x and he couldn't remember a thing afterward. "Why am I in the kitchen? Wasn't I just on the floor?"