I wouldn't worry about it too much, as everyone else here has said, it happens to everyone. My mom still calls me by her oldest brother's name and she's had to deal with me for nearly 34 years now.
It could be worse, I accidentally called my wife by the dog's name (hey, they both start with "T"!) and I don't think she'll ever let me forget it.
Me - 34 year old straight male
Wife of 7 years - 27 year old bi female
- CAUTION: May be scruffy-looking