Basically i have a part-time job as a waiter, this is my first ever job so I'm not the best, But i started of really quite good, but They basically keep cutting my hours from 15 a week down to 4

and because of this i go into work feeling negative and i keep messing up.. like taking food to the wrong table, twice.

So i was thinking of leaving but I'm not sure cos I don't want to mess up like that again because its really embarrassing and a few of my colleagues are complaining about me, So do i stick at it? or write them a letter about wanting to leave? What would you do?
(p.s sorry for this thread, sure you don't really give a sh*t but just need some advice.. thanks)