I understand how you feel. I feel like a bad parent the majority of the time. I used to try harder when my child was younger but it always lead to struggles and disappointments for both of us. He's difficult and I guess so am I.
I always thought I'd be a great mom but I've just accepted how things turned out for the most part and try not to beat myself up too much. You are probably being hard on yourself too. You are not cold hearted or you wouldn't feel or care enough to recognize your thoughts and feelings.