Congrats on your new haircut!
Btw, PainKiller, you could try and cut it gradually. I was afraid too (I have suuuch a babyface, I'm 19 and people always tell me "Oh! I thought you were 12 - 13 - 14!", so...). So, you could try and cut it bit by bit instead of cutting it really short straight away. You could try some sort of haircut to the shoulders, and slowly cutting it a little bit shorter each time. I did had a medium-length haircut and passed with it, though it was at a stage already in which it didn't reached my shoulders. So, if your mother doesn't let you, try a not-so-short cut, maybe it'd help. Or tell her directly that you don't care if it looks good or not.
In the worst case, if you cut it and really don't like the look, it will grow out again and you could use hats and beanies and things like that, specially now that the cold weather will start soon. But, if you do cut your hair, give it a couple days, at the start you could feel weird because it is kind of a big change, so if you think it doesn't look good, after some days you'll probably get used to it and realize it actually does look good.
Well, good look, and don't let your mother's words get to you.