few quick FZ jobs done..

[Mike01]

I have a k&n fitted and the airbox fits perfectly.
First thing I would do is take it out again and refit just to make sure it is sitting correctly, mine is a very snug fit.
Check the rubber (?) moulding round the filter , see if there any small extrusions or such left from the moulding process

I took it out checked and back again many times, will take it out again and check as you say for any excess left round the edges