Must I take Economics for my GCSES before A-levels? If not, will the catching up be difficult?

I did not do A-level Economics, as I did the IB Diploma instead. Having said that, the first few chapters are more or less the same. I also did some self-study on GCSE Economics (though I did not take the exam) before I started, since I was afraid that I did not have the background knowledge. However, it turned out that the first few chapters cover most of what the GCSE syllabus covered, in a more in-depth manner. Also, the pace of the course should be quite reasonable therefore you should not stress about catching up.