Should i confess to the girl i like with a letter?

I've been liking a girl for like 3~4 months now... she goes to my school. we first hung out because my best girl friend is close to her. so she planned to go to the movies and we all went. after that we became kind of close. we talked alot and everything. the girl i like and I are pretty close, we talk alot and text pretty much. but im not sure if she likes me. she sometimes calls me cute(?) and everything but yeah that doesnt mean anything. well recently she found out that everyone in school knew who i liked but not her. so she always asks me who i like. but i always tell her that il tell her later... well thats the story... and its kind of sad cuz summer break has started and she said that she will be out of country for 1 month. but im gonna hang out with her soon before she leaves so i was thinking of confessing my feelings for her with a letter? i want to telll her to read it when she goes out of country and the letter will talk about how i like her and why and yeah. im not gonna ask her out or anything, im just gonna write how i like her. and when she comes back from korea i wanna ask her out. do you think this is a good idea? cuz im not sure. it might be awwkward when she comes back and everything. well she is SUPER nice like super super nice. and shes not mean or anything like that. would she like it?