For one, cast aside romantic intentions from your already girl friends. I doubt any of them consider you anything more, however you never know and often over time friendships can evolve.
Srs tips for meeting new girls & introducing romantic intentions: Make yourself seem busy and that your time is precious - this will show the girl that you are serious about hanging out or whatnot or going on a date rather than just chilling. Also you want to keep the conversation a little flirty, try also avoid areas about her boy troubles and keep some things of you a little mysterious. To begin with don't take things too seriously e.g. messaging every day and saying you'll always be there for her and such, this opens you up to be walked all over.
TL;DR - keep the conversation a little flirty at times (you'll know when it is) and don't open yourself up as just a friend.
Also just chill out, IMO having a girlfriend during the HSC is a no no.. Going on dates or something once in a blue moon is cool but don't get in over head in feels, you don't need that during the HSC.