I feel you. I'm super scared about my upcoming GCSE's in June. I started my revision in the start of Year 11, and reason being is because I was nervous, and that gave me a great motivation boost. Since the start of year 11 up until now, I have improved lots, on my core subjects, but I'm still worried, but that is just an OCPD related problem(I hate English Language, but hopefully I do pass it, with at least a C). You still have 5-6 weeks, use that time wisely, and revise because all that revision can make the difference most definitely.