My QXC was cancelled loads of times before I got to do it - as you're flying on your instructors license they like the forecast to be really good before they let you go.
Flying in low viz is a nightmare - 5 or 6K may sound a lot, but once in the air and into the sun it can be impossible. Bad enough round the local area that you know well, but finding another airfield that you haven't visited before - no thanks.
Remember the saying:
'It's better to me down here wishing you were up there, than up there wishing you were down here.'
Remembering that and acting on it can be the most difficult part of flying.