Passive Aggressive

I wonder if my venting on this is passive aggressive. My boss decided to give my job duties to someone else because I had made mistake on something. But instead of telling me that she was giving away my responsibilities, I just start to notice that I have less to do. I go in and ask her about it, and she blames me and says that it isn't a big deal. I told her that to me it was. I apologized, but nothing else was said. I made the mistake because I wasn't trained otherwise. But I don't dare say that. I went in the office break room and just cried. I have never been in a job in which I have felt so poorly about myself, and my abilities. And it largely has to do with since I am not here all day I have not been trained in everything. I am the type of person that has to understand the in's and out's to truly do the job to the best of my ability. And I don't feel that I have ever received that kind of training. So what I don't understand is why nothing was said to me in the first place. I can fix my mistakes if it is pointed out to me. But I wasn't even given the chance. I feel like I have been slapped in the face. I want to say something to my boss, but I feel like its not a big deal. But it is to me, because I feel less like a good employee. Oh well. There is for venting.