As a teacher’s aide, I have the option of signing up for health insurance that covers abortion and sterilization. Would it be wrong for me to sign up?
No, it would not be wrong for you to sign up. You are paying your premiums to be provided with services you will use; it is not your responsibility how the company spends those premiums. Analogously, in the same way, it would not be your responsibility if the pizza delivery guy used the tip you gave him to buy a pornographic magazine. Your intent is to pay for medical coverage for yourself and/or your family, not to pay for abortion or sterilization.
Of course, if you could find comparable coverage and comparable rates through a company that did not cover abortion or sterilization, it would be best to buy your coverage from that company. However, finding such a company in this day and age is extremely difficult.