I'm really stressed out and scared, somebody who has took an alevel language at GCSE?

So basically i have started my revision for my GCSE's now and I've been focusing primarily on Maths and Science in terms of my mocks as they are by far the hardest. I find English to come quite naturally so i haven't had to do much revision for that or History or Geography either. However, i took my Spanish mock three days ago and although i had kind of forgotten about it and hadn't done any revision apart from a rushed hour the night before, i'm usually quite good at Spanish and have an a/a* controlled assessment portfolio. However, it was so hard! I didn't really understand it and guessed pretty much the whole paper. I really want to know how to secure an A/A* grade at GCSE, what techniques are effective for revising for your listening and reading papers. Its the Edexcel GCSE board Btw. I'm really worried as I feel like i'm not gonna pass. Would be helpful to know how anybody in my situation revised for their exams and got a good grade!
Thanks
BTW Ignore the title - it wont change, i meant at GCSE