Yas and no depends on how you look at it. Lets start by asking this question is sining and calling your self a Christian heretical? Now do you see? its not all black at white. The second point i have to say is that Jesus came to save sinners not those who already followed him by this i am referring to him spending time with sinners for they are ones who need to be saved. So to awser your question if you are actively participating in sin have no remorse for it and reject God yes i would say it would be heretical but if you are genuinely struggling with a sin any sin i would say no. But this is all my opinion and thoughts on the matter so i could be wrong