GCSE's are stressful and the pressure to do well can sometimes be too much. All that matters is that you try your hardest and put in every effort you can to pass them. My solution would be to make a list of subjects to revise in priority order; the ones that are not as important to you at the bottom, and the subjects you need to get where you want to go at the top. Then just make sure to properly revise your top 4 subjects properly and the compulsory ones. Don't stress, or do really long blocks of revision. In between revising do something you like- go out with friends or go for a bike ride or something. It'll then be a bit more broken up and not so stressful.