My two cents worth, from your breif dexription, I dont think that what you did with your hand likely had anything to do with the lines going slack. I would be more interested in alignment of the model. is it square, is it balanced properly, is it flying fast enough. Older models, Ringmasters and such need more airspeed unless they are really light. to heavy, wrong balance, wrong leadouts position, not enough power, these things would be much more likely to cause slack lines in a wingover than how much input you used in your wrist or hand.
For what its worth, here is Paul close up for an idea of what he does with his hand