URGENT HELP - Summer Intern Drug Test

Hi everyone, 

Hope everyone's okay. I'm a junior and I have a "verbal offer" from a $2tn AUM firm. I'm not too sure if that's even called a verbal offer but pretty much HR called me up and said they need me to send a few things, take a drug test and they'll send me the official offer. 

I'm currently in the midwest, where a certain commonly used plant having common side effects such as increase in appetite and cotton mouth is not legal. The firm is headquartered in NYC and I'll intern in NYC too. They've asked me to take a drug test within the next week and I'm shitting bricks. Although I'm not an addict / heavy smoker, I smoked a few times maybe thrice over spring break (13-19 March) and maybe a couple of times after that. The most recent one was about 3 days ago. I'm really worried that I'll end up with a failed drug test for the internship and I have very less time since I've to take it within next week. I've been told, burning fat, sweating it out in the gym, saunas and anti-oxidants are a great idea. I'm one click away from buying a cleansing kit but with this limited time, I'm very worried. I'd sincerely appreciate it if someone could please help me with this. I'm really worried and don't want to blow away this great opportunity. Now yes, people might say that I shouldn't have smoked in the first place but I just assumed I got rejected since they told me I had a super day over a month after my third round of interviews. 

ANY HELP WITH THIS WOULD BE SINCERELY APPRECIATED!!!!! THANK YOU SO MUCH!!!!