If you've been touching it, then there's a good chance it's mother wouldn't want to know anymore. If you haven't then your best bet is to put it back where you found it and keep an eye on it from afar to see if mum comes back for it.
If you keep it, make a thread in the wildlife or 'other pets' sections or PM Feorag on here, she's done a lot of hand rearing if I remember right and she might be able to point you in the right direction.
DEED NOT BREED! SAY NO TO BSL!
The kindness one does for an animal may not change the world, but it WILL change the world for that one animal.