Just remember no matter what something unexpected is going to happen, don't sweat it. As long as it's not a whole bunch of unexpected things in a row you'll be fine.
Besides you are growing a weed, how hard is it to kill a weed ? Weed killers usually don't even kill a weed. It's like a cockroach, you are going to have to try to kill it and then you only have a 50/50 chance.