Worrying is fine. It shows you're human. But why do it? Worrying will not change your results. Surely you'd be happy knowing you've given it a good shot. But if you haven't done anything, as in absolutely nothing, then you have a problem. It is a good thing it seems you've done your homework.
As for the English, I am in a similar boat - although, I did AQA, not Edexcel. We were asked to compare the ways in which people are presented in Vultures and one other poem. I did Half-Caste. Nobody (not one) in my school made that comparison. I must admit, it is not the best of choices, and if I were sitting here with that paper in front of me right now, I would have chosen 'What Were They Like?' but do not worry. The mark scheme does not state which poems should be compared. At all. You will not be marked down for making a strange comparison, and the examiners will be more than happy to read a well structured piece of work about poems they did not expect. So long as you justified your points, you have no reason to worry. Class will show.
I am not sure what to say with regards to History. I also overran with Paper 2 (again AQA not Edexcel), but you'd be surprised what you can knock up in a short amount of time. So you have lost about twenty marks? That does not mean you will fail (well, unless the entire exam is out of twenty, in which case....) but no, you are still right in the game, and your coursework will help.
With Science, do not give up. Don't ever give up. With anything. Failing to prepare is preparing to fail. So long as you do something, it will help. How much depends on how hard you revise.
If you do well in the exam (food) I think it is quite possible for you to get a B - but don't quote me on that.
Hope, somehow, what I have written will help/ease your mind a bit.