Is there something wrong with me?

I came out to my mum as trans a while ago and she reacted really badly which caused me to sort of shove it down for almost two years and recently I've been thinking about it again and her words just stay in the back of my head.
"You can't be trans. Trans people feel like that since they're kids"

I'm not sure if I felt like this since I was a kid but I know how I feel now, but I keep wondering what if there is something wrong with me - that this is just temporary and that if do transition I'll just hate myself and my body like she says.

Any kind of advice would be appreciated.