ECs show multiple things about a candidate:
- Is this a person who gets involved? Penn students are notoriously very active participants on campus.
- Is this a person who achieves things? If provided with resources, can they get things done?
- Do the ECs demonstrate an interest in the school you are applying to?
Your ECs may not be as strong on the third point as you would if all of your ECs were focused on engineering, but they are still very good, and no candidate is perfect. Show some passion in your essays, that can strengthen your case. You have demonstrated a strong knowledge of math and science already.