Sticking gas tasks?

I work at a gas station and at the end of each shift we're suppose to measure the amount of gas out in the tanks. We use a giant ruler that we have to stick down in the tanks. Lately I stopped doing it because I didn't want to cause harm to my baby. 2 of my other coworkers just got in trouble for not doing it and my manager said I was the only one left to talk to. Should I have to stick the tanks? What should I tell her when she talks to me?