Best friends don't reject you. That is the definition of BEST friend. Moving on. Now, did you tell her you LIKED her, liked her? Or just that you liked her as a friend? If the first, maybe she just wasn't ready to deal with that. You are very young, and she may be worried that you won't respect her boundaries. See if you can reassure her that you will respect any boundaries she sets and that you didn't mean to freak her out. Otherwise, chalk it up to experience and find a new friend who will be more ready to accept you as you are. I'm sorry, but sometimes we lose those we thought we could never lose. Not nice, but it happens.
Sometimes some things are just not meant to be, and you have to deal with that and move on as best you can. If you are not straight then why would you like her like her in that way??? That would make you bisexual if that's the case and not actually gay. Which if she knows your gay and you're saying you like her like her in that way then yeah it probably would freak her out a tad! Surely though you can still be friends, if you are best friends after all? Best friends don't tend to stop being friends, but they can fall out very very bad sometimes, but it is usually only because they are that close, and you tend to fall out more with the people that you love the most, so they say, and so I know, but, she probably just needs a little time to come to terms with things, think how she feels about you? Maybe she's confused? Maybe then wasn't the right time to tell her that..dunno..but if you're really best friends and she doesn't like you like you in that way then can you not accept that and still be best friends with her?
Rejecting you how? shut down the friendship its not worth all the stress.
Give her time. She has to get over the shock and when she misses your friendship she will reach out.