Remember that a real supportive friend or parent is supposed to accept you without judgement. They need to know that being part of the community doesn't depend on your interests or if you're smart or depressed or a tomboy or girly. It just happens.
Straight cisgender people say "oh you need more time to to be sure," but then again that makes me wonder how they're in a position to tell you that. (I mean it's not like they know what it feels like to be misgendered or excluded or ignored or bullied for being yourself.) Politely tell them you acknowledge that it takes time to be sure and you weren't sure yourself; you just wanted to let them know since you trust them.
Lol, wait till your 69 and ask if it's been long enough to decide and see what they say.
(P.S. : You probably shouldn't tell teachers anything about yourself unless you know for a fact that they aren't homophobic/transphobic. Like don't even joke about it. It can get creepy... trust me.)