IMHO the problem was probably a control mishandling altering the spin mode. The correct action in this case is to go back to full PRO-SPIN controls for half a turn, then restore recovery actions. Another possibility is that the throttle wasn't fully closed, which can have remarkable effects.
I've not seen this on a C150, but the Bulldog and Tucano will do this without much trouble - they always recover eventually (I do recall a 15 turn eventually once in a Tincano).
I can see the C150 winding itself up too much, but am surprised you think it'll flatten.
G