Could i get into a 15 rated movie?

i am 5'4-5'5. i have broken my voice and it it quite deep, my friends often mistake my voice for a teacher(LOL!). and i want to go to the cinema to see 'paul'. i would go with my siister who is 15 but she thinks i wont get in. i have got a bit of facial hair, like a small moustache which you can see if you are close to me, and some side-burns if you look closely. i have been told i look around 14-15, but i just wanted tips on what to wear. like i usually wear hoodies,joging bottoms ect. but i rarely wear jeans. in my opinion i look about 13-14. i am 12 by the way.what should wear? how should i act? i am going with friends to vue cinema,wood green. two girls( i am the only boy) one looks like she's like 12(she is) and the other looks like 14ish. vue dont care about age, i heard but just in case.