After replacing the standard airfilter with a k+n panel filter I found that the airbox was slightly stretched at the top end and when I snapped the catches on there was a gap between the two plastic panels about 2mm wide with the rubber filter surround wedged in between.Has this happened to anyone else? Might it cause unmetered air to gt in?It seems to have a tight seal against the rubber.

I have just fitted a Jetex performance panel to mine but now problems with the fit. I would carefully tak the air box out and have a good look at it to see what's happened and try to refit correctly

Sounds like the bottom clips on the airbox aren't engaged, shouldn't be any "gaps".

As has already been said, take it all off and carefully make certain it's all gone back right. Check that the filter element is squarely aligned in the lower half of the box, and make sure that when you start to put the top half on, the clips at the lower ends are lined up and engage fully.