Writing your reflection will be much easier if you keep a project log.
Record what you do as you do it - in whatever format is easiest for you, whether in a paper notepad or on your PC or your phone. The notes don't need to be long. Each time you do any work on your project, write down:
1. What have I done today?
2. Why did I do it like that? (ideally this should link with research you've previously read)
3. How did it go?
4. Where do I need to go next?
If you do this as you go along, it will give you a rich source of data for your reflection section, reminding you of things that you'd previously tried and might have forgotten about by the end of the project.