For me, persuasive writing has always been somewhat of a hit or miss. In terms of your writing, I'd just make sure your arguments are sequential in thought - NO RANTING! (that was always my problem), that coupled with some nice language you read in some random newspaper or watch on a Year 5 National spelling bee competition will most likely ensure you wont sound like a primary student lol. I would also recommend to use really fitting connective words and verbs (i.e. challenges, concede, affirm). These kind of verbs and some connective words between arguments/paras will set you apart from the rest. Personally, If i were a marker, I'd rather read a persuasive piece with connections like "developing upon..." or "further supplemented by..." than the over used and bloody annoying "firstly", "secondly", "Furthermore", "Henceforth", "moreover". These words CAN be effective, but try to spice it up a bit is what i'm saying.
And as for a reflection - you can really have fun with this. You can essentially use really strong persuasive analysis - and pick random pieces of your texts and relate the two ('cause english is 'subjective' lol). My advise would be to really familiarise yourself with ethos, pathos and logos. That's all i can really suggest because reflections vary from person to person, and i'm sure you'll nail it along with your persuasive piece. For this section as well, really just sound interested - use language the marker will feel refreshed by - try and put aside the 'common 5' analytical words (portrays, conveys, shows, illustrates, expresses) and use some new ones, idk like: infers, postulates, elicits, depicts, validates. Yeah, so hopefully you see where I'm getting at.
Probably won't be that helpful, but thats my 2 cents haha