You will be absolutely fine, the most important thing in English is to not doubt your abilities, go into the exam thinking you will boss it.
I was so scared about English last year too, I often got 6s and 7s in my mocks and only once achieved an 8 near exam period. Although I was in top set, my teacher marked everyone's papers really harshly and gave us much lower grades than we achieved. This actually made me more determined to achieve the highest grades that I knew I was possible of attaining. You shouldn't let any perceived setbacks affect your performance negatively --- use them to motivate you to do even better. At the end of the day, sets don't matter, when you get your A* in English lit and lang no one will ask you which set you were in. ;-)
Yup, I'm completely with you on that. I find it really difficult to get going in English because I cross things out so much and I'm never satisfied. If you really can't get into the rhythm of starting an essay, I'd recommend having certain sentence starters that you could use as a springboard for all essays. Moreover, if you really find it difficult to form ideas then have some preconceived topics that are really wide and you could write about in any essay (e.g. love/hate in Romeo and Juliet, planning some creative writing pieces in English lang etc.) However, it all boils down to growing in confidence and believing what you're writing is great, if you do then your examiner will too.
Also, I'd heavily advice not 'revising' too intensely for English lang. I didn't revise for it at all, aside from doing mocks and writing a plan for the creating writing section. Those CGP guides and any guides for English lang are a waste of time. Instead, develop your analytical skills in English literature and that will develop your skills in English language. There was this massive correlation where people would achieve high grades in English literature but really low grades in English language, this was because their teacher had spoonfed them the analysis so they never really grew that skill on their own. Don't fall into that trap!
Hope I helped a lil'