Hiya! For your age, your writing is pretty darned good! Try and pick up on punctuation faults early on. The more you read of traditionally-published books (which have usually all been professionally edited), the more you'll absorb the finer points of punctuation etc. If you read masses, writing to the same standard becomes almost instinctive (and relatively effortless!) Alternatively, ask your English teacher to double-check your work - he/she might be delighted that you're into creative writing and have asked for their input!