if you still need help with this, considering the deadline is in a week:
- for why you want to go to brunel, write not about your course, but about what you like about the university. the multiculturalism, the relaxed but supportive atmosphere, the organised open days.
- academic achievements are generally exams as well as things like being house captain, a student mentor, etc
- if youve done any volunteering or part time work, talk about that
- for being a good ambassador, the previous points lead into this. you've learnt leadership and interpersonal skills through things you've done, and you look forwards to representing a uni as modern as brunel
write it like you're certain you're getting the scholarship. don't be arrogant, but sell yourself! i agree with the more structured response, especially because they essentially give you a structure to follow, but make sure you don't relegate your answers into paragraphs following the structure. use it as a guide, but integrate all your points into all your paragraphs so it shows you have some initiative.