Since I went full-time I remember each misgendering incident vividly. In no case do I believe it was done maliciously. The first couple of times were devastating. The last one was just this last weekend. I know it was my own fault due to my presentation, and it was one of those, "sir... ma'am!... sorry!" moments where she immediately corrected herself.
Some people are amazingly good at picking up the tiniest gender cues. They probably don't even know they're doing it, and run with the first thing that enters their head, especially if they're hurried and only get a micro-second glance.
After the first time it happened I came up with a line that I always intended to use if it happened again. Instead of getting belligerent or outing myself, I'd just incredulously ask, "Do I look like a guy to you?!" That would force them to take a closer look, and believe me, Angelique, when anyone looks close, they'll see your true feminine self. They'll either be embarrassed and correct themselves, or, if it was deliberate, will start a showdown, and you can decide whether to escalate the confrontation or not. Having your husband there as an ally would be invaluable to your defense. What I would not do is out myself to them. You are a woman, and admitting you are trans would remove any doubt the people around your misgenderer might have about who is correct.
BTW, I haven't had a chance to use the line yet. The next time it happened was so fast and unexpected I didn't remember it, and this last weekend the situation was self-correcting, so it wasn't necessary.
Good luck, and try not to let it get to you (yes, I should listen to my own advice...).
Stephanie