As a girl with an "extra part", from my own perspective. Sexuality is not fixed, as has been mentioned previously, heterosexuality and homosexuality are the extremes of the spectrum, and they do change with a person.
I started out being sexually attracted to women, but now I am sexually attracted to guys.
Even with attraction, it's to a type of personality which can go beyond gender. Curiosity is a powerful force in re-defining ourselves.
We then also have external definers. The culture (lifestyle) which we select, asks of us.
I could be considered gay from an external perspective, but I do not see my own sexuality as as my gender as an external process, but an internal one.
I know people who see sexuality as defined by those around them, whether straight or other.
I see the original question as: what do you think my sexuality is, based on a (chance) encounter?
In which case I would say, not to sound harsh but to keep it short, lesbo-normative, with some sexual curiosity.