I've just finished GCSE art, as far as I've heard the two are pretty much the same. My first question is, did you take Art at GCSE? If you didn't then I would tell you to prepare to be doing art at least 3 nights a week. Art is very time consuming but as you practice more and get better, you also get faster. Furthermore, if you enjoy art and produce work that you actually want to do, then it'll be easy for you. Watch loads of Art GCSE/A-level youtube videos on A*/A sketchbooks. If you follow their advice you should find it easy. I personally stopped enjoying Art near the end because everyone in that class were with their original group of friends, throughout the year our teacher would tell us our art looked horrible or that we need to throw it away because it made him feel sick, he also favoured abstract work and forced us to not go by our own style so I hated the work I was producing. Hopefully I'll come out with a B because of how bias he is but I would say don't let others demotivate you to do your best.