logistics of negotiating a notice period

maybe this is company dependent but i was wondering if anyone else has been through this and/or has some advice.

i work in an admin role and the notice period in everyone's contract (as far as im aware) is 3 months.

i am waiting for a final offer for a job that i applied to back in march so it has already been a while. but because i havent had the final offer i havent put my notice in or told anyone that im leaving.

i would really not like to stay for a further 3 months, and i dont think it is necessary for my level either.

i know what might happen if i choose to leave earlier on my own terms, but I was wondering how to go about actually negotiating it down. im worried that if i do and they reject me, the 3 months will be a whole lot harder for me. im really keen to get out asap because the job actually gives me a lot of anxiety and im just generally unhappy.

thanks in advance.