Article in Flight Magazine of 24 October 1978 about spins in Cessnas with info from a Cessna test pilot - you should be able to find it online. FAA issued a safety bulletin for instructors on the subject at about the same time based on the same material but more comprehensive.
"Even small amounts of aileron deflection into the spin may increase the rotation rate and prolong recovery."
Info in Rich Stowell's excellent book too.