OK, this is probably too late for your deadline, but you may benefit from it in a future assignment.
First things first - this is an excellent topic. I assume it's from your real life, as that was your assignment. That whole loss of identity and failure to recognise normal landmarks in one's own life is a subject that comes up again and again in literature, in films, in the theatre etc.
The main feature of someone in this condition is not what is there but what is not there. Recognition, memory, logic, consistency - all the things you would expect from an intelligent adult are missing. This should be reflected in the narrative. Your text is short, but it says too much, e.g.
Still walking slowly, he approached her bedside and kneeled down, and tried to put a smile on his face but it was not very believable.
It was not very believable ... well of course not. You're stating the obvious. And then comes the bit the grandmother thinking that Stephen is still a little boy. Is this the first time that Stephen has noticed that the old woman is senile? Why does it have such a violent effect on him? The "punch in the stomach" metaphor is inappropriate. When does sorrow ever feel like a punch in the stomach? Like a cold wind, like an eternal emptiness ... but not a punch in the stomach. I assume you know what a punch in the stomach feels like?
Think about what these moments actually feel like, otherwise the reader is unconvinced.
Other points:
Change the narrator's name. This is an experience from your life, but your name is Steve, so you have failed to address the first requirement of the exercise which was to describe an event in your life as though experienced by a completely different person (that's the whole point of third-person narrative).
Read your text to yourself out loud. Look at this line:
He had a look of dread on his face, as if he knew what everyone else knew but did not want to talk about.
What is a "look of dread"? It's a bit banal. What about "grim determination" or "he felt out of his depth - forced into a role for which he would never be prepared". And then comes the "as if he" bit. This is stating the obvious again. He DOES know what everyone else knows, so you can't say "as if".
And the grandmother's last question "who are you?". Did she really say this? If so, fine, but it doesn't work in this narrative. It hints at a knowledge of her own inability to recognise her own relatives and she can't have that knowledge, because she knows nothing of her own senility. I can't believe she would ask that. She would go back to assuming Stephen is still 6 or start imagining that Stephen is yet another completely different person.
Check your spelling!!!!!!!!!!!!
The bit about the controls of the bed is VERY good. This is the kind of attention to material detail which you should be striving for in the rest of the narrative. The details should express the truth - broad brushstrokes only express the narrator's inner narrative, which means nothing to the reader.
Best of luck
Norman
