I totally understand the thought process behind asking this question and hence I am answering accordingly. Yes, STEM has lesser number of women compared to other fields as nursing or fashion . That's the more the reason to encourage women to join STEM fields.
My favourite thing is get to do what I love. I work as Technical Consulting Engineer and I solve Customer's problems everyday , interact with them and help them through different processes. I strongly believe and studies suggest that a healthy mix of both genders in any field / business helps multiplying the growth. Since you've been a part of an all girls school , initially it might be a little difficult for you to get used to of working with the other gender around and you might be more sensitive to the way they behave or respond to anything. Be rational and practical.
If you are passionate about learning and working in STEM field , don't let your gender be a roadblock. Decide exactly which vertical you want to join and how you want to progress in your career then find a company which helps you with your career aspirations.
As long as you keep learning and excel at your job , anyone else's prejudice shouldn't be a cause of concern.
All the Best!!