Revised version of my opening sentences:
With the unce-unce and manic laughter bleeding into the living room, I could barely think, much less copy my pilfered notes. Labs were due fricking tomorrow—all these rich kids blowing off steam after class clearly indifferent to passing Chemistry or ever getting a big-girl paycheck. But to be honest, had I known then I was about to find myself dead in a dumpster, I might've been in less of a hurry to leave.
There is a lot of good here: a poor kid trying to study while the rich kids study, and moreover a poor kid who's about to get murdered. And well done on the 'big girl paycheck' to signal the MC's gender.
Caveats:
1.
unce-unce -- I am guessing that is supposed to portray a sound, similar to "the
bang-bang of a hammer" or "the
splish-splash of a toddler playing in a puddle" or "the
blurble-blurble-argh of a drowning person"
, but honestly I have no clue what the sound is supposed to portray. Or how to pronounce it (untz? un-say?)
2. bleeding into the living room -- bleeding implies a trickle, a leaking. An annoying background sound. I think if you want it to imply that the sound is deafening, you'll need a different verb. Flooding, hemorrhaging, hammering.....
3. bleeding into the living room -- if she's in the living room, where is this big party happening? I would expect the party to be in the kitchen and living room, and she'd be.... in a back room somewhere? Toilet? Closet? Back garden? And whose house is it anyhow?
4. Agree that sentence 2 reads a bit awkwardly. I'd break it up into two.
5. had I known then I was about to find myself dead in a dumpster -- this is a double edged sword. It's the equivalent of flinging a grenade: it sure as heck gets the reader's attention and signals where the story might be going, but it also can seem a bit gimmicky and delete the suspense in the upcoming scenes since the reader knows what's gonna happen.