where are you thinking of going to uni? £118 a week is double what I paid for the majority of my time at uni, I lived in a cheap city but still... it's a lot - if you can find anything cheaper I'd think carefully about taking it
the other thing to think about is that lots of unis won't return your deposit if you don't achieve a place - so until you have your grades back you're risking it being £200 down the drain (and you'll have to pay another £100-300 at the uni you end up at)
see if you can contact your accommodation department to see how halls typically fill up, my guess is that there will be plenty of spots open when results come out as (if nothing else) plenty of people will have missed their grades so their rooms will free up... although you might have to rush in quickly then or put your name on a waiting list shortly before... some unis have more than enough rooms for 1st years and others have nowhere near enough so it's worth inquiring with someone who knows - there is always a lot of panic about 'making sure you get a room' which makes people make bad decisions about how to get a room and usually the panic is overblown
as for work - keep applying, lower your standards as far as possible - look at call centers as they'll pretty much take anyone, if you're 18 you could try care work, they don't usually have high standards for bank staff, local shops, and think if you have any skills you could sell on a more casual basis (e.g. babysitting, cleaning, tutoring, craft skills etc) and if you have anything to sell
I assume your parents give you some money at the moment given you don't work - maybe you could discuss taking less money and some of it being saved so you can use it for a deposit