Sixth formWatch this thread
And if that doesn't help at all, then one thing that I loved doing was planning and buying stationery for 6th form! It really helped me feel ready and excited about studying A-levels, so if you like stationery, or even if you're only mildly fussed by it, then try having a look around online, although you needn't buy anything yet.
Once you actually start, you'll settle in quickly and have plenty of access to whatever support you might need. For now, keep in touch with your friends and try and get yourself excited rather than nervous, okay?
Good luck, you'll be fine!
I'm in year 12 going into year 13 and I can assure you, 6th Form life is not that bad. Honestly, I feel like I have a closer relationship with my teachers and friends than I did from Yr7 - Yr11. The only major difference you will see is that you will have to be a bit more independent, utilise your time more effectively without a teacher telling you how to.
Another thing in 6th Form that will be in the talks more is university/apprenticeships and careers, especially the personal statement!
Is there anything you are specifically stressed about that I can help you with? The jump from GCSE to A-Level, making friends or your future plans after 6th Form?