tag poppin, i'm with them. how old are you? not gonna be a dick about it because you have a lot of time to learn, but everything there is too big on you. i'd say stick with some tees that come in a small or even smaller (American Apparel, blank fitted tees), some skinnier jeans (Baby GAP), and you should be good.
my only advice: don't stock up on this stuff, puberty is a piece of shit and you'll grow out of all of it very soon.