Like you said, this is a learning experience. It's your first assignment, so it's probably what they call a "formative" assessment (i.e. it doesn't count for anything). It's pressure-free and is designed only to help you improve. That said, your department probably has assessment criteria, so be sure to read it carefully. This will guide you on how to construct your answer.
I get that you obviously want to do well and hit the ground running, but genuinely the best thing is to write it, see what they say and then learn from it. Afterwards, reflect on how you used your notes in the process of writing the assignment, try to see whether it worked or not, and adapt your note-taking accordingly. Maybe you write too much, or too little. Maybe you need bullet points rather than continuous prose. It's a totally personal thing. The entire first year is your opportunity to experiment, and you can only know what changes to make after you've been assessed.
And I think just change your attitude to it as well. You're not in competition with anyone, the lecturers aren't going to put you in a remedial class, or anything like that. If you think about it like that, it can't possibly knock your confidence, because there is absolutely nothing to lose - you only stand to gain information about how to do better next time.