She just wasn't the right person for you. Just because she wasn't into you doesn't mean there's anything wrong with you, you will find someone else I promise <3
You were brave to ask her out. Rejection hurts like hell I know :( . I wish I could make it better for you, but all you can really do is look after yourself until you get through it :( . Be kind to yourself; cry if you need to (but drink lots of water because otherwise it can make you dehydrated and you'll feel ill :/ ), talk to someone.
This sucks, but you will survive, and you will feel okay again; you've got this <3
Honey, relax. It's okay. Women reject guys for a lot of reasons: you could be awkward, she could not be into you physically, she could sense you have a negative attitude, etc. All you can do is stay true and change what you want to better yourself.
You also have to keep in mind that rejection isn't always bad: it shows you two were not compatible, which leaves you open for that potential person in the future who IS right for you.