Depends how many GCSEs you are already doing. If you are doing 9 already then dropping another one is not a good idea, but if you started off doing 10 or 11, you should be alright.
It's always a tough one; would you prefer 9A*s or 9A*s and a B? I doubt it would make that much difference, I'd be inclined to prefer 9A*s but I know someone who got 10A*s and a B, and that B actually gave him another 'point' in the requirements and aided his application.
I think the best thing you can do is pull your finger out and upgrade this coursework to as best as you can. If after your marks come back it isn't as good as you'd hoped, by all means drop it/ consider what you want to do, but for now, just get the work done to the best of your ability, and I'm sure you'll be okay