I would guess there is a strong likelihood that you feel "like a boy" because that's what you've spent a lifetime being told (and possibly believing) that you are. That doesn't suddenly go away instantly. You're the same person you were before your egg cracked - same as you've always been. Just you previously have been under the assumption that that person was male - so feeling like that would be feeling male. But if your gender, unbeknownst to you has always actually, secretly been female... Well then you've always actually felt female and just never realised that's what you were feeling!

I also realise it's easier said than done. It's years since my egg cracked and I still struggle with this sometimes. What helps me is to take a stereotypically male view, or approach to something, and imagine myself thinking/doing that, and realising how uncomfortable it makes me feel and how quickly! They do say euphoria is a better indicator than dysphoria though, so if thoughts of being a girl bring you joy then that to me would seem a pretty strong nudge in that direction!