Hi, welcome to Miniriders,
Drop in and say hello in our Introduce Yourself thread.
http://www.miniriders.com/general-chat/20824-introduce-yourself.html
Does your engine look like this ?
If so, then see the chrome nut in the centre of the bulge on the clutch cover (r/h engine side cover)
That is to adjust the clutch, loosen the nut and then turn the slotted screw in half a turn.
Then while holding the screw still, nip the nut up firm, then start it up and try for neutral.
If it still wont select neutral, try the same thing ^^ again, it might take a couple of goes to get it right.
It shouldn't need to be turned in any more than 2 full turns at the most, if it does the clutch plates could be worn out ?
How many hours has the pit bike done ?
Cheers, Craig