Noooo don't listen to that teacher!! I start Year 12 next week and I've been told endlessly that you should do the subjects you want to do. If you enjoy your A Levels definitely stick to them. I'm taking two of your A Levels, English Lit and Psychology. Because my third A Level is Biology I've been told endlessly I should swap Psychology to Chemistry to open more paths, but I know for a fact that I would hate Chemistry and that I will enjoy Psychology far more instead. So I've been flat out refusing my future Sixth Form, they can't force you to do something you really don't feel like or want to do. So long story short, stick to your A Levels if you like them! The STEM route isn't the only route you can take after all. :' )