I think that I SI to express emotions that I feel I can't express openly to others, as I have major trust issues with people. And the only emotion I seem capable of expressing openly is anger.
I had not cut since I was about 16 or 17 until about a month ago (I'm 47 now) and started up again. I have been in a really depressed state and was hospitalized a couple weeks back for it.
I do have a Pdoc and T now, and also trying to go to group. I have not talked to my T about the cutting. I wanted to last Friday when I saw her but it just never came up... I am embarrassed about it (the SI) after the fact and just couldn't bring myself to tell her.
Have not seen the Pdoc that was assigned to me, yet. So I don't know what he/she will have to say. And obviously nothing about the SI if they don't know.

I hope that you figure out what you need to do to stop doing SI, and also to get the assignment done that you seem to be shying from. Perhaps you should have a family member or close friend there when you write the things out that you need to if you feel that strongly about it.
Peace