Two ideas:
1. Presentation helps. If you do something that makes you look female. Flower in your hair. fake breasts, frilly top, or some feminine accessory like a purse, scarf, or jewelry. Let it speak for you.
2. Instead of saying I'm actually a female, simply correct their pronoun. If someone pronouns you male, or calls you Mr., correct them. Otherwise, doesn't really matter, right?
Hope this helps. In the end, for me this was a major impetus toward transition, so I'd never need to do that sort of explaining.