I agree with you regarding the wide stance. I wasnt/dont feel so comfortable with it but when i raised the subject with the instructor he mentioned that it was just a matter of getting used to it and that the extra width would help with the balance while sucrificing some maneuverability. Dont know about this topic so i guess i should leave it to the experts.
About instability...i cant really recall. Didnt focus on it and only thought about it when i started wiggling.
You said you found yourself not stable. I just simply took the liberty calling it instability. My apologies. But what do you mean by you can't really recall about instability?
The other thing, yes maybe someone should chime in here on the issue of your wide stance. I just think it might be too wide but I don't have any solid facts to quote you unfortunately.