erm...I've never heard of such activity being illegal, but stand to be corrected. It's not quite the same as driving, where there is a clear points structure.
How much of the flight did you actually film? Going solo and flying the approach one handed while fiddling with a cameraphone is never going to be a good idea. Filming a brief bit of enroute footage while in the cruise shouldn't really compromise saftey, and could even enhance the lookout as you look around for the best bits to film. I hope your instructor doesn't find out!