pronoun

 I know the GLOW community has lots of people who are or who know gender fluid and trans persons. I  am writing this comment out of pure ignorance and I am trying to educate myself so please nobody attack me..

I got my makeup done today by a makeup artist. I could tell anatomically this person was born 'male', but had some 'female' (society associated) traits such as haircut, nail polish, and full face of makeup. The artist was wearing androgynous clothing. When talking I reflexively called the makeup artist "he," I caught myself immediately --- but the pronoun was already out there. I could see the artists facial expression was not pleased and I felt terrible that I could have caused offense.  

Two things: should I have apologized for assuming gender, or should I have let it go in hopes of not making things worse? In the future, how should I refer to someone who presents as such? 

My goal is always to give people respect, but I also don't want to bring too much attention to gender and sex with a stranger as I just want them to feel comfortable and normal-bc gender isn't my focus when talking to someone. I'm just trying to figure out how to go about this!