I don't have the official line but I suspect it would be that you can only log your Chipmunk hours if you were flying with a QFI. If not it cannot be considered to be under instruction and you were, legally, no more than a passenger. A trial lesson may not achieve much but you were flying with an FI.
If you falsify your logboook you'll get away with it nine times out of ten. On the tenth time they will catch you and you'll never fly for gain again. Don't do it.