How do you test a mosquito repellent lotion for its effectiveness?

I have this project and our main focus is to make a homemade mosquito repellent lotion made with cirtonella oil. now my teacher's asking me to change it because the procedure on how we're going to test it is not right. If we change the topic, I have to change everything. My hardwork and all the no-sleeping-nights will all go to waste. I cant think of anything else. Please help. :(