sash handle not closing all the way.

[mazperks]

Hi, my upvc side opening sash handle wont close all the way. I suspected toe & heel required so re did that but no joy.
I noticed at the bottom of the opening side there was a definate slight gap where the sash closes onto the vertical frame, and sure enough when pressed from the outside the window closes and latches properly.
Is there a way of adjusting this gap or is it a case of the frame has just warped somehow.
Thanks for any advice Ian.