hey there prince.
sounds like your worried that this girl is way superior to you and that you feel over come by this and who you are. she sounds like a terrific girl but everyone has their negatives, and although you might not see them they will be there. dont feel second to her, we are all equal. you sound like a super person, and maturity doesn't define personality. if your interested in her then try talking to her about how you feel. if she's as nice as you say then you'll be absolutely fine. it sounds like she likes you, and dont frighten yourself by weighing up her positives with yours. we are all different but no one is better. it shouldnt be a competition, you should try and see more good in yourself than just in others.
i have the same problem where i feel i am "too" nice in public, and because i hold in all of my hostility and then i release it at home. i understand that you are afraid that because you are different at home than you are elsewhere, that this "other" person is who you really are. the truth is you have a choice who you want to be. dont change, but just be yourself everywhere. i may sound hypocritical because i have the same worry that although i wish i could be nice ALL the time, i easily explode at home (perhaps because i know that they "have" to accept and love me no matter what). its best to even out everything, and to not try and be something impossible (eg super nice 24/7). we are allowed our outbursts now and then.
so remember that she is no better than you, and she is after all human, so see her as one, and not as some super being. you are just as special, and im sure she knows it.