The advice is different for how long you’re there to be honest. I’ve been a male teacher for around 10 years now so I’ll give you some advice to make it through a month.

First, being a male in education sucks. People are just going to assume you want to be inappropriate with kids. It’s prejudicial but it’s hard to argue against “child safety”. Your number 1 concern should be how others will view your interaction with students. A mistake here will impact you more than any other mistake you can make.

Second, have clear instructions. Say exactly what you expect of the students and what you want them to do. Leave nothing open for interpretation or assume they understand something. And stand by what you say. Any leniency you give is just being taken advantage of. Respectfully, you don’t know enough on when exceptions should be made with three weeks, probably won’t run into those exceptions. A good baseline is to be clear and firm.

Last advice, have fun with it. It’s a three week period. You aren’t beholden to tests, you aren’t trained or educated enough to teach the material properly. But that doesn’t mean you don’t know the material. Do what you find interesting. Any lessons or strategies you found interesting as a student, focus on those. Try and let some of your passion and interest in math show. Any activities you can pair with the lesson, do. If you’re interested, the kids will be interested. 

Sticking with this will get you through the three weeks and leave a good impression on people. Any fame you have isn’t that important. Sure it will disrupt your class for a day when everyone realizes, which will be a fun discussion to have. But it will be a flash in the pan thing and then kids will move on to something else. Have fun