IMHO it is extreemly unlikely that it was an
inverted spin. If you have the stick
back on entry then the spin should be an erect one no matter what your attitude at the time, to get into an inverted spin you need the stick
forward, very difficult to enter inverted on a C150 from normal attitudes,it might flick inverted on entry but if the stick is back then it will still be an erect spin.
The only time I have done an inadvertant inverted spin (not a 150), was from a vertical roll to be followed by a stall turn - stick forward at the end of the roll and rudder in for the S.T.
I do not know about the 150 inverted spin (anyone been there - even a Test Pilot?)but see no reason to say it is impossible to recover from.
If you can get to the UK I would recommend heading for UH at Kemble as they specialise in this sort of training and will be happy to spin you both ways up.
