I'm very pleased you have come here to the Forum. No you do not sound in the least self-centered, you sound like a pretty nice and capable person who has been hit hard by life and is struggling as a result, which is not surprising at all.
Here people will talk to you without hurting you, and for us you crutches and scars are invisible, you are on an equal footing here with every one else in that respect.
Spending 4 months in bed in mostly isolation is in itself a pretty big injury. It has an effect, and leaves you less able to cope, and of course out of date which what everyone else has been up too. It also very much weakens the body.
Surgery to the extent you have undergone it drains the whole system, quite apart from pain and discomfort it takes a toll, and all you resources get used up.
Add to that those crutches, not only conspicuous but also so limiting when it comes to carrying anything, another impediment at the moment. Even getting in a car takes planning.
For someone that mixed quite well with others and did very well at school this is a tremendous change. I'd expect grief, self-doubt, loneliness, frustration and even anger are all there, and are natural and human.
Doing well academically is fine and can stand you in good stead in the future, but if it is ignored by your parents it can seem so pointless and their reaction hurtful. How do you normally get on with them? Sometimes parent can be blinded by their own problems and priories and need reminding of what is important for their sons and daughters. Do you think you might explain to them?
Can I ask if you have spoken to you doctor about these difficulties you face, the depression, anxiety and isolation? Doctors too can concentrate on the physical and not occur to them that they need to treat the whole person, not just the body.
That one boy, well you have just seen an insensitive idiot in action. Unfortunately he, and maybe his mates too, have a lot of growing up to do, and at this stage its lack is at your expense. Try to see him for what he is, superficial, thoughtless and silly.
So how does that new girl get on if she is hated?
At home do you have anyone to be with who cares. maybe a brother or sister, even an auntie?
Can I ask if the coaching was in that class or something else?
I would hope in time you will walk unaided and those scars will fade. Would you like to come back and talk more about things? We would like that.