Not too late at all.
I agree - CGP books are great at GCSE if you can stand the naff jokes.
Remember to do as many practise questions as possible, particularly exam papers!
Don't stress :-) Remember to take breaks every hour or so and go over old material before you start forgetting it.
If you don't have a revision timetable I'd set one up. Make sure you don't put too much content on one day, though. Timetables always seemed like a naff idea to me at GCSE but I found it really helped me to stay on track and stopped me panicking about how much I had left.
If you're doing subjects where you have to learn things like processes, diagrams, formulae etc. I recommend drawing/writing them out and placing them around your room. This helped me with things like maths formulae and biological processes like the nitrogen cycle.
Good luck! :3