I made a mantel clock earlier this year. I recommend that you make detailed notes about each of your design ideas, e.g explain why you chose a certain material and the environmental implications of producing that material. I definitely think you should make a lot of effort on your designing because a large chunk of your marks come from that. I would also recommend a revision guide, CGP is a good one it is available on amazon. It gives you project advice and will help you with your exam which is worth 40%
i also recommend a website called technology student.