Other people may misinterpret my "calming my mind" I'm not an "official" Buddhist but I have accepted the idea that "calming my mind" is good -- by not getting emotional about little setbacks (to the degree I can).  To some degree, I have accomplished this.

As a result, I can keep my head while others are losing theirs.  So far, so good.

But God help me if I get convicted of a serious crime.  Whether I'm remorseful or not (or whether I did it or not), the judge is likely to give me extra punishment if I don't show remorse.

And I once met a friend of a friend with whom I similarly held my reactions in check.  She later described me as being "an emotionless monster" as if I walk around the streets at night eating children and small animals.

What can I do to keep people from thinking something's wrong with me just because I don't get wildly emotional at every little thing?

This question is not off-topic.  Please don't edit it.  Answers that don't directly answer the question as asked will be ignored (no XY-ing, please).
There is a difference between getting wildly emotional at every little thing and having empathy for others. I don't know your friend, or how you interact with her, but I can imagine she may have told you something that was emotional for her and your reaction was deadpan. 

This is not kind. It communicates to another person that their life and suffering is unimportant to you and breaks any social bonds you might have with that person.

It sounds like you are so attached to unattachment that you don't consider how your actions may affect others around you. You can stop people from thinking "something is wrong with you" by forming deep connection with people and showing genuine caring kindness for them.