You will be fine. Weed typically lasts longer than 30 days in heavier individuals. You have a high metabolism and are skinny so I honestly think you have nothing to worry about at all. I personally would say don't waste your money on a home test.. but you say this job is very important to you and you would be in a financial bind if you quit your job and didn't get this new one so i guess it couldn't hurt..

Also, don't worry about being around people who smoke. You cannot test dirty from being around it, secondhand weed smoke has little or no THC in it. The only possible way that you could test dirty from that is if you were in a car with 5 people and they were hotboxing the hell out of it with zero ventilation