I failed my A levels or near enough. Retook one 3 months later, got a B to add to my C and E (yes - not great). But managed to get a Uni place at a Russell Group (but would have been happy anywhere), got a 2:1 and now CEO of something or other and have a very good life (kids, nice house, job, partner, dog, travel etc). Noone has ever asked me about my GCSEs after I went to sixth form college. Noone has ever asked about my A levels after I went to Uni. Noone has cared about my degree three years into first job. Not even sure I would go to Uni these days due to it being a bit of a waste of money ( I have a son there now so know what is offered). Dont worry - all will be fine.
However, revise, do the best you can on the day of your exams but once over, dont sweat it! Many paths to the next stage and the one beyond - life is long but also flies by. Dont waste it worrying.