OK I succeeded in inserting it OK. It didn't feel very uncomfortable, but just not completely comfortable iyswim ... I felt a bit heavy/dragging. Anyway I left it in for about half an hour, then successfully removed it - Phew! 
Do you think I should take is gently, and just try for half an hour at a time, then have a rest. Or should I keep trying until I get it in 'properly' and it feels entirely comfortable?