Thank you all who left advice and their opinions. It has helped me a lot. Going to Aikido tonight to fix the problem. Thank you.
Another question, when I'm performing Tenkan, if uke is resisting - but for the sake of teaching - I find that I have Yonkyo performed on my arm/wrist (skinny wrists and arms).
To ease the problem I've dropped my centre before I tenkan, but I was wondering is there any other advice I could get about this?
(any help would be awesome!