Playing villain in musical...HELP

For some reason I’ve been cast as Cinderella’s wicked stepmother in my school’s production of “Into the Woods.” The directors have made it clear that I’ve been cast, not based on what I’ve been doing, but based on what they think I could do with the role eventually.

The thing is, in order to play a role, one has to tap into certain parts of one’s self. I can do that with lots of things, but evil isn’t one of them. I’m being pushed extremely hard and I would like to think I’m generally pretty versatile, but I really don’t feel comfortable with the way I’m being forced to sing. I feel like if I can’ t make my voice sound the way they want it to naturally I shouldn’t have been cast in the role. I don’t want to permanently damage my voice for a minor role in a high school production.

It’s too late for me to back out, and I’m trying really hard, but it’s extremely exhausting and I really don’t feel like I can give them what they want. Does anyone have any advice? Please!!!