It would appear that the aircraft may not be stalling fully. I remember that some of the C-172's with the drooping leading edge (post 1974) were hard to induce into a spin. If my memory is correct and its the same aircraft you fly all the time, try wings level and power on up to the stall.
If it was a different aircraft to the one you normally fly, it may be rigged slightly different, ie not enough up elevator, to the aircraft you normally fly.