I'm in a very similar situation. My feminine features are causing a lot of male fails, which can be sometimes funny, other times annoying but they are a great confirmation that even when I don't try to present as a girly girl, people still see me as I would like to be seen.
I had the "You cannot use your husband's credit card..." line thrown at me a lot of times in shops so I had to use cash or my other card. I have never tried to prove that I'm a man, even if legally I am at the moment. I just enjoyed that they were sure that I'm a woman.
Last month we were just getting ready to pay after our laser treatment and we told the beautician that we believe we have 20% discount. She looked a little puzzled and asked us the site's name where we found this discount. We told her that it was advertised on the local trans support site that all trans girls have 20% off the regular price. She was like "For both of you? Are you both...?"
At that moment I understood why she was surprised earlier when I asked about hair removal on my forearms.
Two weeks ago I was waiting for my food in KFC and the cashier asked her colleague to finish my order and the guy said "Ok, I'll bring the rest of the order for the lady...".
Sometimes people from other floors at work think I'm a girl and hold the doors for me.
At a previous workplace there were a few funny incidents in the restrooms when I was washing my hands, a guy opens the door, looks at me and says "Sorry, I thought this is the men's room" and leaves or checks the sign on the door again.
If only my voice would be a little better, I probably wouldn't hesitate on going full-time as I pass fine when I put effort in presenting as a female, only my voice fails after some time.