Very few people change presentation for everything all at once, even if it wasn't things out of your control forcing you to put off rl transition, there's no reason you should feel bad changing a gender marker on an internet community so long as it's what you're comfortable with. I was going by male on every part of the internet for about a year before I (legally) changed my name in rl. I don't think it's insincere if it's what you really feel, and you shouldn't feel you owe anybody anything.
I'm going to stop there, because I could go on forever about sincerity and integrity and gender in a ciscentric world and 'owing people' your 'real' gender, I really could, but this is probably not the place.
Regards,
John, Lord of Zombie Hordes and Cats
(p.s. It can also useful to wave at reluctant friends and therapists/gatekeepers, like "but I'm [insert gender] at [the internet/youth group/friendship circle] and it's what feels right/better/best/ect". But really, just go with whatever feels more comfortable. I'm stopping, really.)
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You should always be in touch with your inner magic ninja weasel.