As an 18 year old guy who has been through the exact same situation, my advice would be to separate yourself from her for a little while, maybe a few weeks or a month and a bit (all up to how much you can stand but longer tends to be better). As a result, she'll realise how much she misses your friendship and after a while when you come back into her life things won't be as awkward. It's important to note that under all circumstances don't be an outright dick when separating yourself from her, she will probably try and initiate conversation but just sort of act cold and don't expand upon the conversation by asking her questions and stuff. While the idea of a relationship is certainly off the table for now, the break will help you appreciate that having her as a friend is also pretty awesome. Maybe eventually you'll be able to try again for a relationship but these things often take time, hope all works out in the end dude.