Nicky, I am still puzzled by your HV! That's great news that the weight gain is fine - and 8 oz is fine, and the very top end of what anyone would expect in 5 days, so no worries at all there. In fact it's 7 oz, so again we're with the dodgy metric/imperial translation thing!
"Hv said she'd like to see her back at her birth centile "
WHY?
There is nothing magical about a birth centile.
Anyone who understands about these things knows not to place any significance on the birth centile.
In fact it is misleading to do so. If you're feeling brave, ask her why the birth centile is so significant for her.
"She suggested comfort milk top ups if she's unsettled."
WHY? Why top ups? WHY comfort milk?
" I think maybe she's just small?? "
Not especially - the 9th centile is a perfectly fine centile to be on :) In any case, I don't think she is reading the chart properly. She's only a shade under the 25th centile anyway.