A 15 year old girl who likes to sing. Thanks!
Don’t mind the hand motion, when we sing our whole body works, if putting your hand up, tilting your head, closing your eyes or whatsoever helps you, just do it. Regarding the singing, you have good vocal projection and tone, now, in the verses and in the first 2 chorus, that’s where you should use your falsetto for the high notes, so that you can save your energy and the power of your voice to the actual belting parts of the song which is usually in the bridge onwards. don’t mind if the original singer hit the note in falsetto or not, you’re your own singer, try to sing this again with the falsetto in the beginning and I bet you’ll be able to hit the “at the top of my lungs” note in ease and relaxed (Mandy Moore hit that note with her head voice, BTW. not falsetto).
your over-all voice and tonal quality is great for a 15 year old, if not, mature enough. what you just need to work on now is the use of your falsetto / head voice and make it connected to your natural tone for easy transitions and for it to sound similar to each other… you can work on it via vocalization. vocalize regularly and you’ll see big improvements… other than that, you have good voice quality and power, it’s just a matter of voice placements for you now. :D