Is this note she gave me for my bday sicnere or not?

The letter sounds sincere to me.. Maybe she's being distant because she's afraid of her feelings she has for you. She might feel like you're going to meet someone new at collage and she's avoiding you hurting her in the future... so she's acting like she hates you so she doesn't get hurt, instead you do. I don't know, I'm sorry. It really seems like she genuinely liked/likes you and doesn't want to get hurt.