Can someone check the opening of my story?

I’m in a hospital bed with my mum gripping her hand onto mine. All I have endured is an extensive amount of excruciating agony of aching pain, within my joints. All that’s in my head is the constant thudding and thumping sounds, echoing consecutively. It all began in a maths classroom...
“Tic Toc, Tic Toc.” The clock dragged its second hand towards the number nine as if being pressurised towards danger. (Perhaps, it was because I was in maths and it was getting a thrill out of traumatising me to stay in this classroom longer than I wanted to.) It knew how desperate I was to...get...out...of...this class.
Miss Tedious (the most lacklustre teacher ever) was talking algebraic garbage but her voice just seemed a blur. Her eyes seemed to sag with an expression of dullness and lack of life. Her mouth moved robotically. Her body slumped against the classroom wall beside the whiteboard, hoping for the lesson to end (just what I was hoping). She definitely had no sense of fashion that day, as she wore her lengthy, mustard skirt and a gaudy knitted jumper, with those horrifying rusted specs.
The room stood silent.
I sat near the steamed window, gazing outside. I saw a rusted, sapphire Nissan parking in one of the bays, under a bare tree, which seemed to have been taking a shower, with all the rain pouring down from the overcast of clouds. The car door slammed shut.

I can't figure out why you are using all those words to describe this setting. It is wordy, is the nice way of saying it. However, I am uncertain what your assignment was on this, perhaps it was to be colorful and descriptive. However, I think you have over-killed the setting by a large number of words.

Take the first paragraph, for instance.
<< It all began in a Maths classroom, and it led me here to the hospital and excruiating, throbbing pain. It began in the classroom...

I was in Maths class, bored, and distracted beyond description. The teacher was rambling on in Algebra talk which blurred in my conscientiousness. Out the window next to me, I saw a rested Nissan parking, then the car door slammed shut.

Now look at this comparing it to yours. Did you really have a purpose in
- describing the teacher
- commenting on her sense of fashion
-the tree taking a shower
- the room standing (sic) silent

I slashed that away, but if it is needed, add it, but I suspect it is not a part of the story.