In my opinion its mainly how you wear it like, if you have confidence your gunna look good, because its like everyone else at your school is wearing it too, but if you carry yourself like you think you look good people are gunna think you look good. =)
Than the other little thing is like you need to accessorize lol, get like a ribbon that matches, and like tie it around your head, wear it with some heels if your allowed, and I'm not sure if you want to look hot or just look more attractive, because if you mean hot than your gunna look like a skank by wearing your skirt oober short and all, but cute just have it a little shorter, and for your shirt you could just pin it so it fits a little better.
Like I wear skirts at my school that aren't really dress code, and my shirts are low because I unfortunately have giant boobs with like a tiny waist ha, but I never get in trouble because I carry myself like I am confident but I'm not like oh look at me and my t*ts and legs, like I look innocent I guess ha and cute. So you probably could get away with it if you carry yourself with confidence but like with a smile and act cute not hot. lol ya I don't know if this helped but I really hope it did, good luck with your uniform. =)